Chemical Reactions -key concepts student guide 9 SCIENCE Name__
YeaR 9 chemical reactions

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Key Concepts


  1. 1. Patterns, order and organisation
  2. 2. Form and function
  3. 3. Stability and change
  4. 4. Matter and energy
NAME:

Science Quest
TEXTBOOK
SCIENCE Quest PRACTICALS / ACTIVITIES
SCIENCE Quest
HOMEWORK
OTHER ACTIVITIES/RESOURCES
1
7 Chemical reactions
INQUIRY: INVESTIGATION 7.1 Reflecting on a burning candle p273
The chemistry of eating

Readiness Test Chapter 7
https://www.tes.com/lessons/OC4zw9705Grb_Q/
2
7.1 Rearrange those atoms
page 274
INQUIRY: INVESTIGATION 7.2 EXP: Conserve that mass!
Questions: p275 1-8
7.1 Combustion
Words to Learn
Reactants, products,
Conservation of massexternal image placeholder?w=200&h=50
Progress Test 7.1 Homework
3
7.2 Matter and energy: Chemical reactions and energy
page 258
INQUIRY: INVESTIGATION 7.3 EXP: Exothermic and endothermic processes
Questions: p279 1-4, 8-10
7.2 Campsite chillout
EXTENSION:
P279 Q13 or 14
Words to Learn
Exothermic
Endothermic

Progress Test 7.2 Homework
4
7.3 Acids and bases
page 280
INQUIRY: INVESTIGATION 7.4 EXP: Antacids in action
INQUIRY: INVESTIGATION 7.5 EXP: Reaction of acids with metals
EXTRA EXP: Making your own indicator
Questions: p284 3-6, 9,10,13,19,20
7.3 Acids and bases
Investigation;
The case of the unidentified solutions. (worksheet)
Words to Learn
Interactivity
Play the pH rainbow in your eBookPLUS and drop liquids into their correct position on the pH scale. int-0101
5
7.4 Acid rain
page 285
Science as a human endeavour
INQUIRY: INVESTIGATION 7.6 Investigating acid rain
eLesson
The rain is burning!
See some of the destruction that acid rain has caused on Earth. Learn why acid rain is created and how we can stop it from occurring. eles-0065
7.6 EXP: Investigating Acid Rain
Questions: p269 1-5

7.4 Acid rain

Yr9 Acid rain task
Assignment: prove to me you know all there is to know about acid rain
Progress Test 7.4
Homework

Complete this as part of a pretest
remember to put your class infront of your first name.

Access Code is 9ABHW

Test Link http://www.classroomclipboard.com/490625/Test/52C0DB1038B64DB597640C23FC220715
6
7.5 Combustion reactions
page 287
Questions: p288 1-5, 6, 9

Combustion Reactions
http://www.youtube.com/watch?v=UygUcMkRy_c
7.5 Airship up in flames
design an expt to measure the energy released when the following is combusted-tea light,wood, paper, metho,
-weigh before and after keeping variables constant
- use a variety of thermometers
to measure the temp increase - eg digital, electronic infrared gun and glass
Words to Learn

Progress Test 7.5
Homework

some help for design your expt
7
REVISION
ICT Activity: page 276
ProjectsPLUS
ChemQuiz!
Design and run your own game show. pro-0107
Revision: p275 Q 1-3, 5-10, 13-18
Individual Pathways
Activity 7.1 Revising chemicalreactions
Activity 7.2 Investigating chemicalreactions
Activity 7.3 Investigatingchemical reactionsfurther
Writing chemical formulae of compounds in symbol form


Class Notes Chemical reactions


Burning match observation

When the match burnt we saw - smoke, colour change and heat was given off - these are indications that a chemical reaction has occurred.
IN a chemical reaction the chemical that are mixed together at the start of the reaction are called the reactants. The things that are made are called the products.

The law of conservation of mass

says that matter can neither be created nor destroyed in a chemical reaction. the elements are rearranged to form new products. From this law we can also say that the atoms of elements that form the product of a reaction must be found as atoms of elements on the reactant side of the equation


Conservation of Mass Prac report


Aim
Method
1. draw the apparatus label all relevant parts
2. initial weight of reactants - record in results
3. weight after reaction - record in results

Results
Observations
1.
2.
3.
etc

Data


Conclusion

If the masses are different suggest a reason why. If the masses are the same suggest a reason why.


End of prac report
_


Example
alka seltza tablets and the water were the reactants. when we weighed them before they reacted together they all weighed 122g. When we mixed them together lots of gas bubbled out of the water. This gas was one of the products. The mass of the all the products were 122g.
The mass had not changed - this proved the law of conservation of mass.


Writing Equations for reactions
In Chemistry we often write a word equation or molecular formula equation to explain what has happened in the chemical reaction. These equations show how the reactants have recombined to form new products.

reactant is
a product is

A Chemical Reaction occurs when two or more reactants react to produce one or more products. This may cause bubbles to form ( gas is given off), temperature change (exothermic or endothermic) change of colour or a new product may appear.

A chemical reaction is described by the following word equation:
images
images


Exothermic reactions and endothermic reactions

Exothermic reactions give out heat (or sound or light) Energy (or sometimes all of these - eg an explosion. Exothermic reactions make the thermometers go up. Eg Acid and magnesium. The temp of the soultion went up - exothermic.

Endothermic reactions take in energy making their surroundings colder. The thermometer goes down.
Eg Potassium Chloride and water - the whole testtube gets cold- the thermometre went down. this is endothermic

An airbag explodes -Endo or exo?

Acids and Bases


Acids are chemicals that are sour and corrosive. They have a pH of less than 7 . they are used in industry, they react with metals to produce hydrogen gas and a salt.
Bases are slippery and have a pH of more than 7
Water is nether an acid or a base - it is neutral and has a pH of 7
Acids and Bases reactions
An Acid + Base ----------> Salt + Water

Common acids and bases||~ Acid
Uses
Hydrochloric acid
  • To clean the surface of iron during its manufacture
  • Food processing
Nitric acid
  • The manufacture of fertilisers, dyes, drugs and explosives
Sulfuric acid
  • The manufacture of fertilisers, plastics, paints, drugs, detergents and paper
  • Petroleum refining and metallurgy
Citric acid
  • Present in citrus fruits such as oranges and lemons
  • Used in the food industry and the manufacture of some pharmaceuticals
Carbonic acid
  • Formed when carbon dioxide gas dissolves in water; present in fizzy drinks
Acetic acid
  • Found in vinegar
  • The production of other chemicals, including aspirin

Base
Uses
Sodium hydroxide (caustic soda)
  • The manufacture of soap
  • As a cleaning agent
Ammonia
  • The manufacture of fertilisers and in cleaning agents
Sodium bicarbonate
  • To make cakes rise when they cook
>

pH Scale and determining Acids and Bases


This scale tells us the strength of the acid or base. The scale goes from 0 to 14. Any compound registering below 7

Is called an acid. Weak acids have a pH of 4 to 6 ( vinegar). Strong acids have a pH of 0 to 3 (HCl or sulphuric or nitric acids).

Compounds with a pH of 8 to 10 are basic or alkaline eg blood or soda water, some detergents.

Compounds with a pH of 11 to 14 are strong bases egs are ammonium, dishwashing powder, NaOH.
Water is neutral and has a pH of 7.
Indicators
An indicator will change colour in the presence of an acid and will change to a different colour in the presence of a base.
Universal indicator goes red in an acid , green in water (neutral) purple in base. It also changes to a yellow in a weak acid and a blue/ green in a weak base.



ACID + ANTACID PRACTICAL

DISCUSS AND EXPLAIN
1. What was the mass of the antacid powder? 1g
2. What colour change occurs when the methyl orange indicator is in the acid? red in acid and goes orange when no acid is there.
3. By subtraction, calculate the mass of antacid used to neutralise 50 mL of dilute hydrochloric acid. =1g
4. How does your result agree with other groups in your class? Suggest reasons for the similarities or differences between your results. Different colours of orange were expected by the different groups
5. Use your results to calculate how much antacid you would need to neutralise 500 mL of dilute hydrochloric acid.
If 1g is needed for 50 mLs then _10g is needed for 500mL
The reaction was a neutralisation reaction.
Acid + base ----> salt + water
2HCl + Mg(OH)2 ------> Mg Cl2 + 2 H2O
The reaction that caused the bubbles was
Acid + carbonate ----> salt + water + carbon dioxide

example Calcium carbonate + Hydrochloric acid -----> Calcium Chloride + carbon dioxide + water

INQUIRY: INVESTIGATION 7.5

Reaction of acids with metals

When an acid reacts with a metal, a salt is formed and hydrogen gas is given off. You can test for hydrogen gas by holding a lighted match at the mouth of the test tube. If the gas is hydrogen, it will explode and make a ‘pop’ sound.
• Place a small piece of one of the metals in a test tube.
• Add the acid to the test tube to a depth of 1 cm.
• Observe the chemical reaction.
• Test for hydrogen gas by holding a rubber stopper over the end of the test tube for a few seconds and then placing a lighted match at the mouth of the test tube.
CAUTION: Do not push the stopper into the test tube firmly. Just hold it in the top of the test tube for a few seconds.
• Record your observations. ----
• Repeat the test with other metals.
DISCUSS AND EXPLAIN
1. When zinc metal reacts with hydrochloric acid, zinc chloride and hydrogen gas are formed. Write a word equation for this reaction.

ZInc + Hydrochloric acid ----> Zinc Chloride + Hydrogen gas

1. When the lighted match produces a ‘pop', the hydrogen gas is reacting with the oxygen in the air to form water. You may have noticed the water form at the top of the test tube after you performed the match test. Write a word equation for this chemical reaction.

Hydrogen gas + Oxygen gas ---------> water

Combustion Reactions
The General equations for a combustion reaction is
Organic material + oxygen ------> water + Carbon Dioxide

eg Methane gas + oxygen ----> water + carbon dioxide



Testing the acidity of household substances

Aim:

Method

1 Test with red litmus by adding one drop of substance and record
2 Test with blue litmus by adding one drop of substance and record
3 Test with universal indicator by adding one drop of indicator to 3 mL of substance record the colour. NB solids will need to be dissolved at the ratio of one grain of rice size to 3 mL of water.

Results

Substance
Red litmus turned
Blue Litmus turned
Universal indicator turned
Water
nc
nc
green
Lemonade
r
r
orange
Lemon Juice
r
r
red
Vinegar
r
r
red
Salt
nc
nc
green
Sodium Bicarbonate
b
nc
blue/aqua
detergent
b
r
blue/purple
Conclusion
The following were acidic; Lemonade, lemon juice, vinegar and of these lemonade was not as acidic as the others according to our universal indicator results red being more acidic than orange or yellow.
The following were basic; Sodium bicarbonate, detergent -
The following were neutral; water, salt

RED litmus always turns blue in a base or alkali and will turn back to red in an acid
BLUE litmus always turns red in an acid and will turn back to bue if dipped into a base or alkali
UNIVERSAL INDICATOR gives us a range of colours from RED (strong acid) to orange and yellow (weak acid) to GREEN (neutral) to aqua for weak bases to blue and purple for strong bases and alkalis


Designing an expt to measure the energy output of fuels

Background

When fuels are burnt an exothermic reaction occurs. A general form of this reaction can be written as; Fuel + oxygen ------> water + carbon dioxide + heat energy

Heat can change the temperature of water. The energy required to heat 1 gram pf water 1 degree celsius is 4.2 Joule. We call this the specific heat of water.

Therefore heat energy out put can be calculated by
Heat Energy = Mass of water X 4.2 X Temp change.

Aim

Hypothesis

Method
1. variables to keep constant are; height of fuel from the water, mass of water,


Results
Fuel
Variable
Before
After
Change
Calculations of Energy output per gram
candle
mass of water





temperature





mass




wood
mass of water





temp





mass




paper
mass of water
10
10
0
HeatEnergy = mass of water x 4.2 x temp change

temp
15
40
25
Heat energy = 10 x 4.2 x 25
= 1400 Joules per 0.5 g

mass
10g
9.5g
0.5g
heat energy per gram =2800/g








Extra notes---- Beyond the level


Writing Chemical Formula of compounds
Solution means in water = (aq)

Step 1. Determine the symbol and charge of each ion (the numerals in () represent the ion’s charge) but write the cation (+ ions) before the non-metal anion(s) (- ions) except for substances with acetate.


CATIONS



ANIONS

1+
2+
3+
1-
2-
3-
Ammonium NH4+
Barium Ba2+
Aluminium Al3+
Bicarbonate HCO3-
Carbonate CO32-
Nitride N3-
Cuprous (I) Cu+
Beryllium Be2+
Chromium Cr3+
Bromide Br-
Chromate CrO42-
Phosphate PO43-
Hydrogen H+
Calcium Ca2+
Ferric (III) Fe3+
Chloride Cl-
Dichromate Cr2O72-
Phosphide P3-
Lithium Li+
Copper (II) Cu2+

Chlorate ClO3-
Zincate Zn(OH)42-

Potassium K+
Iron (II) Fe2+

Permanganate MnO4-
Silicate SiO32-

Silver Ag+
Lead (II) Pb2+

Acetate CH3COO-
Oxide O2-

Sodium Na+
Magnesium Mg2+

Fluoride F-
Peroxide O22-


Strontium Sr2+

Hydride H-
Sulfate SO42-


Tin Sn2+

Hydroxide OH-
Sulfide S2-


Zinc Zn2+

Iodide I-
Sulfite SO32-


Mercury Hg2+

Nitrate NO3-
Thiosulfate S2O32-




Nitrite NO2-



Step 2. To write a chemical formula, write ONE of each ion & balance the ion charges so the total is 0 by writing the required coefficient to the bottom right of the ion. For multiples of an atom group, use ( ).
eg. Al3+Cl-, Charge number of Al is a 3 and the charge number of Cl is a 1 so Al1Cl3 but write it as AlCl3
eg. Pb2+NO3- . Charge number on Pb is a 2, and NO3 is only a 1 so Pb1(NO3)2 but write it as Pb(NO3)2.

Another way to do this is to remember the hook and eye model
Remember the cations have hooks - the anions have eyes.
draw the cations with their hooks and then join these with the eyes of the anions. Keep adding cations or anions until there are no empty hooks or eyes.
This will show the number of cations and anions that will combine to form the compound.

Eg.CaCl2.jpg














NaCl.jpg



Class notes

Physical or Chemical change

Expt



Results

Chemical
Observation
RESULTS
CaCO3
White powder no change
NC
Mg + HNO3
Bubbled and cloudy
Hydrogen gas given off
Chemical Change
Pb(NO3)2 + KI
Turned yellow
Chemical Change
HNO3 + NaOH
Got warmer
Chemical Change
CuSO4 + Mg
Mg Turned Black, Cu ions attached to the Mg
Chemical Change



We know a chemical change has occurred if we see one or more of the following;

Colour change

Gas or bubbles given off

Change in Temperature – (getting hotter or colder)

New product formed – eg a precipitate or metal deposit



Write an outline of the light sticks experiment p 54

Chemiluminesence – Chemical change that produces light as the result of a chemical reaction.



If it was put into hot water – it got brighter because the molecules sped up and bumped into lots of other

molecules make a stronger reaction. The cold water slowed the reaction down and so less light was

emitted. Animal can produce this as well and we call this bioluminescence.



Solubility

When a salt dissolves in water it is said to dissociate – this means the ions that make up the salt will float freely in the water as

Cations or anions. Eg NaCl -à Na + and Cl- ions.



Characteristics of chemical classes

  1. Acids – All acids contain hydrogen and usually a non metal or a non metal oxide. (Phosphate – P and O = PO4 3- this makes phosphoric acid)

H3PO4 Other examples of acids are Sulphuric acid H2SO4, Nitric acid HNO3 , Hydrochloric acid HCl, Hydrofluoric Acid HF, Vinegar or acetic acid or

Ethanoic acid CH3COOH



  1. Bases or Alkalis – These contain a metal combined with a hydroxide group -(OH) Examples of these are MgOH2,

AlOH3, ZnOH2, NaOH



  1. Salts – This is a general name for the substance formed by an ionic bond between a metal and a non metal

Example MgCl2, NaCl, CaCl2, MgSO4



4.The nitrates – these are compounds joined by an ionic bond between a metal and the nitrate complex anion. Eg NaNO3, Ca(NO3)2



  1. Sulfates – these are compounds joined by an ionic bond between a metal and the sulfate complex anion. Eg MgSO4, CuSO4







Types of reactions

Neutralisation – This is a reaction between a acid and a base (or alkali) –When an acid reacts with a base they neutralise each other.

The products formed are a salt and water.



Do these

Hydrochloric acid + sodium Hydroxide ---à



Nitric acid + Calcium Hydroxide --->





Sulfuric acid + potassium hydroxide -à





Precipitation reactions

These are any reaction that forms a solid that might continue to float in the solution – The best example is

KI (aq) + Pb (NO3)2 (aq) ---> KNO3 (aq) + PbI2 (s) This makes the bright yellow specks that we made in our experiment.





The subscripts that are in brackets behind a chemical formula indicates the state of the chemical in the reaction.



(s) means solid

(l) means liquid

(g) means gas

(aq) means aqueous – aqueous means dissolved in water generally resulting in ions floating in the water.





Combustion Reactions

This type of reaction always combines oxygen with another compound or element to make an oxide ( ie oxygen combined

With a metal or nonmetal like carbon)

Eg Methane + oxygen à carbon dioxide and water



Eg2 Magnesium + oxygen à magnesium oxide





pH Scale and determining Acids and Bases

This scale tells us the strength of the acid or base. The scale goes from 0 to 14. Any compound registering below 7

Is called an acid. Weak acids have a pH of 4 to 6 ( vinegar). Strong acids have a pH of 0 to 3 (HCl or sulphuric or nitric acids).

Compounds with a pH of 8 to 10 are basic or alkaline eg blood or soda water, some detergents.

Compounds with a pH of 11 to 14 are strong bases egs are ammonium, dishwashing powder, NaOH.



Water is neutral and has a pH of 7.



Different bonds

Ionic bonds – these are between metal and non metals – found in salts. This is where one element donates an electron to

Another element eg NaCl

Covalent bonds – this is where two or more non metals share electrons eg Carbon dioxide , water,

Metallic bonds – are the ways metal atoms join together to make a slab of metal. They are described as a lattice of cations

Floating in a sea of electrons.