Ch.13.3 Flashcards
Name the precautionary measures of decomposition of water by electricity.
Wear safety goggles
Wear protective gloves
Handle acid with care
Wash your hands thoroughly after the experiment
Read the steps of decomposition of water by electricity.
- Label two test tubes A and B. Fill them with pure water.
- Invert the test tubes and place test tubes A and B onto the anode and cathode of an electrolytic cell respectively. Fill the electrolytic cell with pure water. Add 5cm³ of dilute sulphuric acid to the pure water.
- Turn on the power supply.
- After 10 minutes, turn off the power supply. Stopper test tubes A and B quickly.
- Remove the stopper from test tube A and quickly put a glowing splint into the tube. The glowing splint relights; therefore, we know that the gas collected in test tube A is oxygen.
- Remove the stopper from test tube B and quickly put a burning splint near the mouth of the tube. The burning splint burns with a pop sound; therefore, we know that the gas collected in test tube B is hydrogen.
What is the use of dilute sulphuric acid in the decomposition of water by electricity?
The acid is used to increase the electrical conductivity.
What is the use of an electrolytic cell in the decomposition of water by electricity?
An electrolytic cell is used so that electricity can be supplied for the decomposition of water.
In the decomposition of water by electricity, why must the gas collected in test tubes A and B be ___________ and _____________ respectively?
oxygen, hydrogen;
this is because H2O slightly ionises to form H⁺ and OH⁻ ions; OH⁻ ions are given electrons at the anode to form oxygen, while H⁺ ions are given electrons at the cathode to form hydrogen.
What are the names of the positive and negative electrodes/poles of an electrolytic cell respectively?
Anode and cathode.
What is the working principle of electrolysis? Does this mean that electrolysis only works on ionic compounds? Support your answer with an example and explanation.
The transfer of electrons. No, it doesn’t. Water is an example of a non-ionic compound that can be electrolysed because it can slightly ionise to form H⁺ and OH⁻ ions.
Water, a ______________, can be broken down into ______________ and ______________ by ____________________________.
compound, hydrogen, oxygen, passing electricity through it
What are ionic compounds composed of?
A cation and an anion, usually the ions of a metal and non-metal.
A compound is ________________________________________________________.
a substance made up of two more more elements
Compounds can be ________________________________________________________ by ______________(a)______________. However, elements cannot be __________________________________________ by (a). Name an example of this.
broken down into its constituent elements, chemical methods; broken down into anything simpler; we cannot break down oxygen molecules into oxygen atoms.
Chemical methods involve ____________________________. Name an example of this.
chemical change; decomposition by electricity, or electrolysis
Are all compounds made up of molecules? Explain.
No. An example of a type of compound that is not made up of molecules is ionic compounds.
Many ___________________________ are compounds. Name three examples.
common substances; water, table salt, carbon dioxide
What is true for the chemical formulas of all compounds?
They must contain more than 1 chemical symbol.
Name 6 common compounds, their chemical formula and their constituent elements.
Water, H2O, hydrogen and oxygen Table salt, NaCl, sodium and chlorine Carbon dioxide, CO2, carbon and oxygen Glucose, C6H12O6, carbon, hydrogen and oxygen Quartz, SiO2, silicon and oxygen Chalk, CaCO3, calcium, carbon and oxygen
Read the following procedure for investigating the properties of a compound — iron(II) sulphide — and its constituent elements.
- Put two spoonfuls of iron fillings into a boiling tube with a spatula. Add two spoonfuls of sulphur powder in another boiling tube with a spatula. Observe and record their colours.
- Fix the boiling tube containing iron fillings with a stand and a clamp. Put a bar magnet near the bottom of the boiling tube and move the bar magnet upwards. Observe and record if the bar magnet attracts the iron fillings.
- Repeat step 2 with sulphur powder instead of iron fillings.
- Pour the iron fillings into the boiling tube containing sulphur powder. Tap the boiling tube to mix them thoroughly. Record the colour of the mixture.
- Repeat step 2 with the mixture of iron fillings and sulphur powder.
- Place a piece of rocksil in the mouth of the boiling tube containing the mixture. Heat the mixture strongly with a non-luminous flame. Turn off the Bunsen burner immediately when the mixture glows or smoke comes out of the boiling tube. Iron (II) sulphide has been formed from iron and sulphur in the boiling tube.
- Put the boiling tube in the test tube rack and allow the iron(II) sulphide to cool. Observe and record the colour of iron(II) sulphide.
- Repeat step 2 with iron(II) sulphide instead of iron fillings.
Why is rocksil placed in the mouth of the boiling tube containing iron fillings and sulphur powder in the experiment of investigating the properties of a compound — iron(II) sulphide — and its constituent elements?
Rocksil is used to prevent the potential exchange of gas to in turn prevent the leakage of sulphur or sulphur dioxide gas, which are harmful to the human body, and to produce the maximum amount of product.
Name the required safety precautions in the step of creating iron(II) sulphide in the experiment of investigating the properties of a compound — iron(II) sulphide — and its constituent elements.
Perform this step in the fume cupboard
During heating, don’t point the mouth of the boiling tube to anyone
Wear safety goggles
What are the colours of iron fillings, sulphur powder, the mixture of iron fillings and sulphur powder, and iron(II) sulphide as observed in the experiment of investigating the properties of a compound — iron(II) sulphide — and its constituent elements?
dark grey, yellow, yellowish grey, black
