Chemical Changes

Question 1

Give the general word equation for the reaction between an acid and a base

Answer 1

Acid+base->salt +water

Question 2

What type of reagent could be used to show that an acid or base has been completely neutralised

Answer 2

When an acid neutralises a base the products are neutral and have a pH of 7. Therefore an indicator can be used to show that a neutralisation reaction is over

Question 3

Describe the steps involved in carrying out a titration

Answer 3

To find concentration of some alkali use a pipette and pipette filler and add a set volume of alkali to a conical flask and add indicator. Use a funnel to fill a burette with some acid of known concentration. Record the initial volume of the acid in the burette. Using the burette add the acid to the alkali a bit at a time. The indicator changes colour when all the alkali has been neutralised. Record the final volume of acid in the burette and calculate volume of acid used to neutralise the alkali.

Question 4

Why should you first carry out a rough titration when carrying out a titration experiment

Answer 4

To get an approximate idea of where the solution changes colour

Question 5

Why shouldnt you use Universal indicator as an indicator in a titration

Answer 5

Because you want to see a sudden colour change in a titration and universal indicator changes colour gradually.

Question 6

Name two suitable indicators for a titration between an acid and an alkali and state their colours in acidic and alkaline solutions

Answer 6

Litmus-Blue in alkalis and red in acids
Phenolphthalein-pink in alkalis and colourless in acids
Methyl orange-Yellow in alkalis and red in acids

Question 7

What is a strong acid

Answer 7

Strong acids ionise completely in water and all acid particles dissociate to release H+ ions

Question 8

By what factors does the H+ concentration increase for a decrease of 1 on the pH scale

Answer 8

For every decrease of 1 on the pH scale the concentration of H+ ions increases by a factor of 10

Question 9

Explain the difference between a strong acid and a concentrated one

Answer 9

The larger the amount of acid there is in a certain volume of liquid the more concentrated the acid is. The strength of an acid tells you what proportion of the acid molecules ionise in water. pH will decrease with increasing acid concentration

Question 10

Write a balanced equation for the reaction between hydrochloric acid and sodium carbonate

Answer 10

2Hcl + Na2CO3 –> CO2 + 2Nacl + H2O

Question 11

What is a base

Answer 11

An alkali that dissolved in water to form a solution with a pH greater than 7. Alkalis form OH- ions in water

Question 12

Is zinc more or less reactive than iron

Answer 12

More reactive

Question 13

What is the general word equation for the reaction of a metal with an acid

Answer 13

Acid + Metal –> Salt + Hydrogen

Question 14

Give the balanced equation for the reaction of calcium with water

Answer 14

Ca + 2H2O –> Ca(HO)2 + H2

Question 15

Will copper react with water

Answer 15

No because copper is a less reactive metal

Question 16

What product forms in the oxidation of magnesium by oxygen

Answer 16

Magnesium is oxidised to make magnesium oxide

Question 17

Explain how you decide wether a metal can be extracted from its oxide by reduction with carbon

Answer 17

The position of the metal in the reactivity series determines wither it can be extracted by reduction with carbon. If it is lower than carbon it can be reduced with carbon.

Question 18

Why is gold found as itself in the earth

Answer 18

Because they are so unreactive they are in the earth as the metal itself

Question 19

In terms of electrons give the definition of oxidation and reduction and explain the term REDOX

Answer 19

Oxidation-A loss of electrons
Reduction-A gain of electrons
REDuction and OXidation happen at the same time.

Question 20

In a displacement reaction, does the metal atom get reduced or oxidised?

Answer 20

The more metal ATOM loses electrons therefore it’s oxidised. The metal ION is reduced

Question 21

What is an ionic equation

Answer 21

An ionic equation shows only the useful bits of reaction. Only the particles that react and the products are shown.

Question 22

During electrolysis which electrode are the positive ions attracted to

Answer 22

Cathode

Question 23

Why can ionic solids not undergo electrolysis

Answer 23

Because they are in fixed positions and can’t move

Question 24

Do ions get reduced or oxidised at the anode

Answer 24

Oxidised

Question 25

During the manufacture of aluminium from bauxite which electrode is aluminium formed at

Answer 25

Cathode

Question 26

In what situation will hydrogen gas be given out during the electrolysis of an aqueous solution of an ionic solid

Answer 26

If H+ ions and metal ions are present hydrogen gas will be produced if the metal ions form an elemental metal that is more reactive than hydrogen

Question 27

If halide ions are present in an aqueous solution of an ionic solid will oxygen gas be released.

Answer 27

No as molecules of chlorine bromine of iodine will be formed.

Question 28

What test could you use to determine if hydrogen gas has been produced in an electrolysis reaction

Answer 28

Hydrogen will make a “squeaky pop” with a lighted splint