Reactions Of Acids, temperature changes that occur

Question 1

Three properties of acids

Answer 1

• They are soluble
  • They release H+ ions when dissolved in water
  • They all have a pH less than 7

Question 2

How come acids have characteristic reactions?

Answer 2

Due to their ability to release H+ ions, all acids have characteristic reactions

Question 3

Method of reacting magnesium in acid (5)

Answer 3

• Fill the basin and test-tube with water, let the test tube rest on the bottom of the basin
• Measure 15 cm3 of hydrochloric acid using the measuring cylinder and add to the boiling tube 3.
• Add the magnesium strip to the boiling tube – ensuring that the magnesium is fully immersed in the acid by swirling and allow the reaction to proceed for 10s
• After 10s, place the delivery tube onto the boiling tube and place the end of the glass tube underneath the test-tube. Hold the test-tube upright and collect the gas produced. Once the test- tube is full, stopper the tube and place it in the test-tube rack.
• Light a splint. Remove the stopper of the test-tube and hold the lit split at the top of the test- tube.

Question 4

Observations as magnesium reacts with acid ? (3)

Answer 4

• Bubbles of gas
  2. Magnesium disappears
  3. Heat given off

Question 5

What did you observe when you collected and tested the gas? (3)

Answer 5

1. Colourless, odourless gas
2. The gas has a low density – rises upwards
3. Lit splint hear squeaky pop

Question 6

When you collected the gas you should have noticed that it rises to the top of the test-tube and also that the water in the basin has no effect on the gas. Why is this ?

Answer 6

This is because hydrogen is less dense than air and insoluble in water.

Question 7

Balanced symbol equation and ionic equation

Answer 7

Balanced symbol equation
Mg + 2HCl —> MgCl2 + H2
Write the ionic equation for the reaction and include state symbols.
Mg + 2H+ —> Mg2+ + H2

Question 8

Observations when Copper (ii) oxide is reached with sulfuric acid (2)

Answer 8

• Solution turns from colourless to blue

- Unreacted black copper oxide remains at the bottom of the beaker

Question 9

Why was the pH higher after the experiment with sulfuric acid and copper (ii) oxide ?

Answer 9

The pH is higher because a neutralisation reaction has taken place.
acid + base —> salt + water

Question 10

Write the balanced symbol equation for the reaction between copper(II) oxide and sulfuric acid.

Answer 10

CuO + H2SO4 —>CuSO4 + H2O

Question 11

Describe the reaction between an acid (hydrochloric acid) and an alkali (sodium hydroxide) (3)

Answer 11

• During this reaction the H+ ions from the acid and the OH- ions from the alkali react together to form water.
• As this happens, energy is released which is detected by the thermometer.
• This means that the reaction is exothermic (the ‘exit’ of energy).

Question 12

Why do you think we use a polystyrene cup to carry out the reaction between an acid and alkali reaction?

Answer 12

Polystyrene is an insulator and will not absorb the heat given out by the reaction.

Question 13

Observations of reactions between calcium carbonate and hydrochloric acid (5)

Answer 13

• Bubbles of gas given off
• calcium carbonate disappears
• heat given off
• gas produced is more dense than air and does not escape.
• The gas bubbled through limewater changes from colourless to milky.

Question 14

Write the balanced symbol equation for the reaction between the calcium carbonate and hydrochloric acid.

Answer 14

CaCO3 + 2HCl—> CaCl2 + H2O + CO2

Question 15

Write the equation for the reaction of carbon dioxide with limewater. Include state symbols.

Answer 15

CO2(g) + Ca(OH)2 (aq) —> CaCO3 (s) + H2O (l)