224cm3
168cm3
112cm3
100cm3
Correct answer is B
1mole of gas at STP = 22.4dm\(^3\)
0.0075 mole of CaCO3 = xdm\(^3\)
cross multiply;
where 22.4dm\(^3\) = 22400cm\(^3\)
x * 1 = 0.0075 * 22400 → 168cm\(^3\)
the gas CO2 which evolved was gotten from CaCO3 so we use the number of moles of CaCO3 only
33%
44%
55%
87%
Correct answer is B
molar mass of water [7H\(_2\)O] = 7[ 2 * 1 + 16] → 7 * 18 = 126g/mol
molar mass of ZnSO\(_4\).7H\(_2\)O = [65 * 1] + [32 * 1] + [16 * 4] + 7[ 2 * 1 + 16]
→ 65 + 32 + 64 + 126 = 287g/mol
percentage of water of crystallization = \(\frac{mass of water of crystallization}{mass of hydrated compound} * 100%\)
→ \(\frac{126}{287} * 100\) = 43.9
≈ 44%
Which of the following is a physical change?
Freezing ice cream
dissolving calcium in water
burning kerosene
Exposing white phosphorus to air
Correct answer is A
Freezing is a physical change. It involves a liquid changing states to a solid. Thus, freezing a substance will not change its chemical identity, but its state.
A mixture of sugar and sulphur can be separated by?
dissolution in water, evapouration and filtration
filtration, evaporation and dissolution in water
dissolution in water, filtration and evaporation
evaporation, dissolution in water and filtration
Correct answer is C
Sulfur is insoluble in water but sugar is soluble.
Hence; dissolution of sugar to have sulfur as the only insoluble solid.
Filtration: The filtrate is the liquid that passes through the filtration filter. Meanwhile, the residue is the solid that remains on the filtration filter.
Evaporation: water as part of the filtrate changes into a gas to leave sugar as residue.
Detergents are manufactured with straight hydrocarbon chains so as to make them
soluble
biodegradable
cheaper
foamy
Correct answer is B
The choice of straight hydrocarbon chains primarily serves the purpose of enhancing the biodegradability of the detergent, making it less harmful to the environment once it is washed away.Since unbranched (i.e., straight) chains are more prone to attack by bacteria, therefore in most of the detergents used these days, the branching is kept to be minimum so that the detergents become easily biodegradable.