1. investigating the reactions of acids Flashcards
(4 cards)
hydrogen gas when reacted with a metal
Apparatus and chemicals
Boiling tube
Delivery tube
Test tube, basin
Test-tube rack
Measuring cylinder (25 cm3)
Safety glasses
Wooden splint
1 mol/dm3 hydrochloric acid (15 cm3)
2 cm strip of magnesium
Method
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.
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 10 seconds, 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.
Observations
In this reaction it is very obvious that a gas is produced – you can see fizzing in the boiling tube.
The magnesium also disappears, it is being chemically changed and forming a soluble product.
You may have also noticed that the boiling tube becomes warm, this is evidence that heat is given off during the reaction.
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.
This is because hydrogen is less dense than air and insoluble in water.
You will also have heard a squeaky pop when the lit splint is placed into the test-tube.
This is actually a mini explosion!
The hydrogen is reacting with the oxygen in the air and making water – you may have seen little droplets of water on the side of the test-tube after the reaction.
Metal oxide reactions with acid
Apparatus and chemicals
Kettle
250 cm3 beaker
100 cm3 beaker
Measuring cylinder
Spatula, watch glass, glass rod
Heatproof mat
Safety goggles
Sulfuric acid 0.5 mol/dm3
Copper(II) oxide (2 g)
pH paper
Method
Using pH paper determine the pH of the acid at the start, record this in your results.
Using a measuring cylinder, measure out 25 cm3 of sulfuric acid into the small beaker.
Collect approximately 2 g of copper(II) oxide on a watch glass.
Using hot water from a kettle, fill 1/3 of the larger beaker with hot water.
Warm the sulfuric acid beaker by letting it rest (carefully) in the hot water bath (leave for 2 min).
Carefully remove the small beaker and add copper(II) oxide to the acid slowly, stir with a glass rod.
Keep adding the copper(II) oxide, until there is some left over at the bottom of the beaker. Let the beaker sit for 2 min to allow the black powder to settle.
Observations
In this experiment, you should be able to observe that at the start the acid has a pH of about 1-2.
Also, although there is no gas produced, there is a chemical reaction taking place as the solution changes from colourless to a pale blue, you should also notice that the copper(II) oxide disappears at the start.
However, once all the acid has reacted, the copper(II) oxide remains behind as seen by black powder at the bottom of the beaker. The blue colour is due to the formation of a soluble salt.
Reaction of acids that produce heat
Apparatus and chemicals
Polystyrene cup and lid
250 cm3 beaker
Thermometer
Measuring cylinder (25cm3)
1 mol/dm3 HCl (25cm3)
1 mol/dm3 NaOH (25cm3)
Method
Place the polystyrene cup into the 250 cm3 beaker to stabilise it.
Carefully measure 25 cm3 of hydrochloric and place it in the polystyrene cup.
Take the initial temperature of the hydrochloric acid and record it in the results table.
Wash out the measuring cylinder and rinse it with a little sodium hydroxide solution.
Then measure 25 cm3 of sodium hydroxide solution into the measuring cylinder.
Add the sodium hydroxide solution to the acid, stir with the thermometer, measure and record the highest temperature reached during the reaction.
Reaction of acids with a metal carbonate
Apparatus and chemicals
Measuring cylinder
Boiling tube, test-tube
Disposable pipette/dropper
Test-tube rack
HCl 0.5 mol/dm3
Calcium carbonate (3 g)
Limewater (5 cm3)
Method
Using a measuring cylinder, measuring 15 cm3 of hydrochloric acid and place into the boiling tube.
Using a clean measuring cylinder, measure 5 cm3 of limewater and place into a test-tube. Place the test-tube and boiling tube side by side in a test-tube rack.
Carefully add the calcium carbonate to the acid – record your observations.
Using the disposable pipette/dropper, collect the gas produced by opening and closing the dropper above the reaction in the boiling tube.
Once the gas has been collected in the disposable pipette/dropper, bubble the gas through the limewater and record your observations.
Observations
During this reaction, it is very obvious that gas is produced as the reaction fizzes vigorously. The carbon dioxide gas is more dense than air which allows us to use a dropper to collect it – it will not rise out of the boiling tube quickly and so can be collected and bubble through the limewater. Once the carbon dioxide gas goes through the limewater it reacts with it and makes a solid (precipitate), this causes the limewater to go ‘milky’.
