6. Deduce the formula of calcium phosphate. [1]
Calcium has a charge of +2 (Ca²⁺) and the phosphate ion (PO₄³⁻) has a charge of -3. To balance the charges, we need three calcium ions and two phosphate ions. Hence, the formula for calcium phosphate is:
Ca₃(PO₄)₂
1.7 Draw a ‘dot-and-cross’ diagram of the carbon disulfide molecule. Show outer electrons only. [2]
For the carbon disulfide (CS₂) molecule, carbon (C) has 4 outer electrons and sulfur (S) has 6 outer electrons. In the dot-and-cross diagram, we can represent this as follows:
S : : : S
X C
X X
: X :
- 'X' represents the electrons from carbon.
- ':' represents the electrons from sulfur.
- Each sulfur atom shares the electrons to form a double bond with carbon.
1.8.1 Explain why adding chlorine makes water safe to drink. [1]
Adding chlorine to water kills bacteria and other pathogens, thus disinfecting the water and making it safe to drink.
1.8.2 Describe a chemical test for chlorine. [2]
To test for chlorine gas, you can use a piece of damp litmus paper. Chlorine gas will bleach the litmus paper, turning blue litmus paper pink or white, indicating the presence of chlorine.
1.8.3 State and explain one use of argon. [1]
Use of Argon: Argon is commonly used in welding processes.
Explanation: Argon is an inert gas, which means it does not react with other substances. In welding, argon provides an inert atmosphere that prevents oxidation of the metals being welded, resulting in a cleaner and more effective weld.
1 answer