09 Test for Gases

01 Test for Carbon Dioxide Gas

Expected Observation: Effervescence observed. A colourless and odorless gas evolved produced white precipitate in limewater. (No writing of chalky or milky or white suspension!!!) 

02 Test for Ammonia Gas 

Expected Observation: Effervescence observed. A colourless and pungent gas evolved turn damp red litmus paper blue.

03 Test for Oxygen Gas 

Expected Observation: A colourless and odorless gas evolved relights a glowing splint.

04 Test for Hydrogen Gas 

Expected Observation: Effervescence observed. A colourless and odorless gas evolved extinguishes lighted splint with a 'pop' sound.

08 Writing Word Equations for Acid Reaction...

01 Chemical Properties of Acid 

a) Acids react with reactive metals to form salts and hydrogen gas. 

b) Acids react with metal carbonates to form salts, carbon dioxide and water. 

c) Acids react with bases to form salts and water. 

With the help of the given examples below, write down any five possible reactions given the list of substances that can occur given in the link provided here. Write down suitable word equations representing the reactions. 

02 Acids + Reactive Metal -> Salts + Hydrogen gas 

E.g. Sulfuric acid + Sodium -> Sodium sulfate* + Hydrogen gas

* Sulfate because it consists of atoms of sulfur and oxygen.

03 Acids + Metal Carbonate -> Salts + Carbon dioxide + Water 

E.g. Nitric acid + Potassium carbonate* -> Potassium nitrate + carbon dioxide + water

*carbonates consist of atoms of carbon and oxygen bonded together.

04 Acids + Bases/Alkalis -> Salts + Water : Type of Reaction: Neutralisation reaction 

E.g. Hydrochloric acid + Sodium hydroxide -> Sodium chloride + water

07 Differences in Chemical Properties between Acids and Bases

Instructions: Watch the videos below for the various reaction of acids and bases with other substances. You may recall some of the observations made during your practical lessons. Make relevant observations and write suitable equations to represent the reaction. Write your answers in the link provided here. 

A summary of basic knowledge of Acids, Bases and Indicators are included here. 

1. Acids + Reactive Metals (Group I, II or III,  Zinc or Iron etc) --> salt + hydrogen gas 

E.g. Reactions of various metals with hydrochloric acid

2. Acids + Metal Carbonates --> salt + water  + carbon dioxide gas 

E.g. Calcium carbonate with acid

 3. Acids + Base  --> Salt + water (a form of neutralisation reaction) 

E.g. Titration of hydrochloric acid with sodium hydroxide

4. Alkalis + Ammonium salts --> salt + ammonia gas + water 

E.g. ammonium chloride + sodium hydroxide  --> sodium chloride + ammonia gas + water

06 General Differences between Acids and Bases - Differences between Acids & Bases

01 Activity - Finding the General Differences between Acids & Bases

In this group activity, you will research as a group to find the differences between acids and bases. Do find out also about salts, alkali and carbonates as well to make connection between them.

You will present your research finding via a mind map through mindmeister. Log on to mindmeister and register via your facebook account or create a new account. The link is here.

A raw sample can be viewed here.

Please complete your mind map within the stipulated time and paste your link into this document here.

Some common names of Acid, Bases, Carbonates, Salts etc You must know:
(Take note of those highlighted in red)

Acids	Bases		Metal Carbonates	Metal hydrogen carbonates	Salts
	Alkalis (Soluble)	Insoluble Bases			Salts containing metal ions	Ammonium salts
Hydrochloric acid	sodium hydroxide	copper (II) oxide	sodium carbonate	sodium hydrogen carbonate	sodium chloride	ammonium chloride
sulfuric acid	potassium hydroxide	copper (II) hydroxide	magnesium carbonate	potassium hydrogen carbonate	potassium iodide	ammonium nitrate
nitric acid	ammonium hydroxide	aluminium oxide	calcium carbonate		lead (II) nitrate
phosphoric acid	lithium hydroxide	lead (II) oxide	copper (II) carbonate		copper (II) sulfate
citric acid	calcium hydroxide (slightly soluble)	zinc oxide	zinc carbonate		Copper (II) nitrate
tartaric acid		lead (II) hydroxide	lead (II) carbonate		calcium sulfate
ethanoic acid		magnesium oxide	ammonium carbonate		barium sulfate

Gases you must know:

Ammonia	Hydrogen	Oxygen	Chlorine
Nitrogen	Steam	Carbon dioxide	Carbon monoxide

05 Changes in Temperature of the Surrounding

01 Temperature Changes of Surrounding due to Energy Changes During Reaction 

Chemical Changes are accompanied by a change in energy. When energy is given off during the reaction, temperature of the surrounding increases. When energy is absorbed during the reaction, the temperature of the surrounding decreases. 

02 Interpreting Temperature-Time Graph of Surroundings during Reaction 

a) For Reaction involving absorption of energy into the system: 

Energy is taken into the system when reaction is taking place. The thermometer recording the temperature recorded shows the temperature of surrounding temperature. Since energy is taken into the system, the surrounding temperature decreases. However, after the completion of reaction, temperature increases as heat is now released from the system for the system to reach thermal equilibrium with the surrounding. The room temperature is 25 degree Celsius. 

Examples of Changes involving absorption of energy: Boiling, Melting, Sublimation, dissolving, decomposition etc... 

b) For Reaction involving release of energy into the system: 

Energy is released to the system when reaction is taking place. The thermometer recording the temperature recorded shows the temperature of surrounding temperature. Since energy is removed from the system, the surrounding temperature increases. However, after the completion of reaction, temperature decreases as heat is now taken into the system for the system to reach thermal equilibrium with the surrounding. The room temperature is 25 degree Celsius. 

Examples of Changes involving release of energy: Combustion, photosynthesis, freezing, condensation etc... 

04 Writing Word Equations for Chemical Reactions

01 Interpreting Word & Chemical Equations:

In the reaction of the combustion of carbon to form carbon dioxide:

Carbon + oxygen gas -> Carbon dioxide gas [Word Equation]

Carbon and oxygen gas are reactants. Carbon dioxide gas is the product.

C (s)     +   O2  (g) -> CO2  (g)  [Chemical Equation]

C and O are chemical symbols of carbon and oxygen element.
Oxygen is a diatomic molecule so it appears as O2 . 
(s) and (g) are called state symbols ; they represent the state of the substance during the reaction.

You will learn more about writing chemical equations later. Now, you just focus on writing word equations. 

02) How do we write the name of the compound formed? 

Referring to the notes of naming compounds : Click here for recap on naming compounds.

03) Word Equation of Combination 

a) Sodium + chlorine gas -> sodium chloride
b) iron + sulfur -> iron sulfide
c) magnesium + oxygen -> magnesium oxide

04) Word Equation of Combustion/Rusting 

a) Combustion of Fuels:
i) Methane gas + oxygen gas -> carbon dioxide gas + water

b) Rusting of Iron 
Iron + oxygen -> Iron (III) oxide

Note: iron (III) refers to the charge the iron has when forming a compound with oxygen. It means it has a charge of 3+. You will study the charges of each element when forming compound later on. You will only need to write this (I), (II)  or (III) etc for certain elements. 

05) Word Equation of Decomposition 

a) Copper (II) Carbonate -> Copper (II) oxide + carbon dioxide
b) Zinc nitrate -> zinc oxide + nitrogen dioxide + oxygen
c) Water -> hydrogen + oxygen (Electrolysis)

06) Word Equation of Precipitation 

a) lead (II) nitrate + potassium iodide -> potassium nitrate + lead (II) iodide (yellow precipitate) 
b) copper (II) nitrate + sodium hydroxide --> copper (II) hydroxide (blue precipitate) + sodium nitrate

07 Complete the Exercise in this link provided as a group.

03 Types of Chemical Reactions

01) Types of Chemical Changes/Reactions 

a) Combustion  
b) Combination 
c) Decomposition 
d) Precipitation Reaction 
e) Acids & Bases Reaction (will be covered later) 
f) Photosynthesis 
g) Respiration 

Watch the videos below and answer the questions for each reaction in this link (click here) as a group. Each group will be assigned a reaction later on to present to class. You may recall your laboratory experiences to help you answer the questions. 

Additional Slides are provided here. 

a) Combustion 
Example 1: Burning sodium in oxygen

Example 2: Burning methane in oxygen

                                       


b) Combination 
Example: Sodium reacting with chlorine gas to form sodium chloride (tablet salt)

c) Decomposition - i) Thermal Decomposition 
Example: Thermal Decomposition of Copper (II) Carbonate

c) Decomposition - ii) Electrolytic Decomposition 
Example: Electrolysis of water

d) Precipitation Reaction 
Example: Formation of lead (II) iodide precipitate

e) Respiration 
- How to determine amount of carbon dioxide evolved?

02 What is a Chemical Change & Activity 01 Classification of Chemical Changes

01) What is a chemical change?
A chemical change is a process that produces a new substance. The particles of the substance are broken apart and the atoms are rearranged into new particles, forming a new substance.

For example: Combustion of propane gas

02) Types of Chemical Changes/Reactions 

a) Combination 
b) Combustion
c) Decomposition 
d) Precipitation Reaction 
e) Acids & Bases Reaction 
f) Photosynthesis 
g) Respiration 

03) Activity 1 - Classifying Chemical Reactions 

Referring to activity 1 - Classifying Chemical Reactions (click here to access folder), go to 203_01_Classifying Chemical Reactions classify the equations according to categories as a group of three. After doing so, predict the classification used by other groups assigned for your group. The classification of the chemical reactions are listed on 02 Types of Chemical Changes/Reactions but at this point of time, you may also choose to classify in your own way based on the observation of the equations.

01 Chemical Changes Lesson Objectives

Knowledge and skills

 Knowledge – At the end of this unit, students must understand that:

·         A chemical change is a process that produces a new substance. The particles of the substance are broken apart and the atoms are rearranged into new particles, forming a new substance.

·         Chemical changes are accompanied by a change in energy. When energy is given off during the reaction, the temperature increases. When energy is absorbed during the reaction, the temperature decreases.

·         Chemical changes may result in observations such as colour change, effervescence and/or formation of precipitate.

·         Acids turn blue litmus red, has a sour taste and a pH of less than 7.

·         Alkalis (soluble bases) turn red litmus blue, has a bitter taste and a pH of more than 7.

·         Bases are metal oxides and hydroxides. Alkalis are soluble bases.

Skills – At the end of this unit, students must be able to:

·         Identify different types of chemical changes. These include combination, combustion, decomposition, acids and base reactions and some biological reactions (photosynthesis and respiration).

·         Predict that products of a chemical reaction, given the reactants, and vice versa. Example: zinc + hydrochloric acid à zinc chloride + hydrogen gas.

·         Distinguish between physical and chemical changes.

·         Test for gases such as carbon dioxide, ammonia, hydrogen and oxygen.

·         Describe the test for carbon dioxide, ammonia, oxygen and hydrogen. For example, carbon dioxide is tested using limewater, where a white precipitate in limewater indicates the presence of carbon dioxide.

·         Describe chemical changes using word equations.