I've 2 questions:-
(1) An element is a good conductor of electricity and forms a chloride which dissolves readily in water. Its hydroxide dissolves in strong acids and strong alkalis. What is this element?
a. aluminium b. calcium c. lead d. magnesium
(2) A lorry carrying nitric acid overturned and some of the acid was spilled on the road. Which substance, when added in excess would neutralize the acid without leaving an alkaline solution?
a. sodium hydroxide b. calcium carbonate c. sodium carbonate d. water
Hope someone can explain why that option is the answer. Thanx!!!
1) Dissolves in strong acid and alkalis. At O Level, you need to know that it means it can react with both acid and alkali.
When reacted with acid, it 'acts' like an alkali; and when reacted with alikali, it 'acts' like an acid. The type we called it "amphoteric". In your syllabus, you need to know the basic 3 amphoteric metal (at higher level, there are much more). The 3 are
Zinc, Aluminium, Lead.
To answer question (1), you need to know your solubility table for Chlorides. For all level, it is "All chloride soluble in water except silver, lead, mercury.
The answer to question (1) is Aluminium.
2) option (d) is out, because it can't neutralize nitric acid. Left with (a), (b), (c).
When sodium hydroxide (a) is added in excess, you will get an alkali solutions. The neutralization is of the acid-base reaction. Option (a) is out.
Left with option (b) and (c).
Both calcium carbonate (b) and sodium carbonate (c). Now check the solubility table for carbonates. You will see "All group I carbonates are soluble, the rest are insoluble".
If Sodium carbonate is added in excess, it will results in alkali solution being it is soluble in water (by-product of neutralization). Option (c) is out.
The answer is Calcium Carbonate (b) because
1) Neutralization. Calcium Carbonate + Nitric Acid -> Calcium Nitrate + Water + CO2.
Excess Calcium carbonate will remain as solid lumps (won't dissolve in water). Thus not creating alkali environment.
Answer for question (2) is b.
Hey, I'm sorry you to trouble you with this, but im encountering some difficulties in my O's chemistry. hope you can enlighten me.
1. 20cm3 of oxygen reacted with 20cm3 of carbon monoxide. what are the volumes of the gases remaining, at the original temp and pressure?
The ans is oxygen-10cm3 carbon monoxide-0cm3 and carbondioxide-30cm3. Why is this so?
2.what has a mass equal to that of one mole of water?
a. 24dm3 of water
b.one mole of steam
c. one molecule of water
d.2 moles of hydrogen molecules and one mole of oxygen molecules.
why is the answer B?
3. What is the mass of aluminium in 204g of aluminium oxide,al2o3(numbers are in sub script)
a.26g
b.27g
c.54g
d.108g
how do i get to the answer d?
4. What do both an atom and an ion of the isotope of sodium contain?
the ans is 12 neutrons. I uds that the neutron for the atom is 12 but for the isotope why is it 12 as well, i thought isotopes have diff number of neutrons?
Well these are very useful questions but I am student of commerce I guess the answer of first one is calcium and second is calcium carbonate, I am not sure.
1. 20cm3 of
oxygen reacted with 20cm3 of carbon monoxide. what are the volumes
of the gases remaining, at the original temp and pressure?
The ans is oxygen-10cm3 carbon monoxide-0cm3 and
carbondioxide-30cm3. Why is this so?
Equation: 2CO + O2 ---> 2CO2
So oxygen is in excess since ratio of CO : O2 is 2:1
So actually 10 cm3 of O2 is left, no oxygen is left but 20cm3 of CO2 is formed going by the chemical reaction
2.what has a mass equal to that of one mole of water?
a. 24dm3 of water
b.one mole of steam
c. one molecule of water
d.2 moles of hydrogen molecules and one mole of oxygen
molecules. why is the answer B?
Going to assume that water is in liquid state.
so 1 mol of H2O has volume of 18 g, assuming density =1g/cm3
2H2 + O2 ----> 2H2O
so (d) = 2 mol h2O
so ans is b because 1 mol of steam = 1 mol of water since steam is just gaseous water
3. What is the mass of aluminium in 204g of aluminium
oxide,al2o3(numbers are in sub script)
a.26g
b.27g
c.54g
d.108g
how do i get to the answer d?
Ar(Al) = 27, Ar(O)= 16, so Mr(Al2O3) = 54+48 = 102
so 204 g = 2mol Al2O3
1 mol Al2O3 contains 2mol Al
2 mol al2O3 =4 mol Al = 4x 27 = 108 g
4. What do both an atom and an ion of the isotope of sodium
contain?
the ans is 12 neutrons. I uds that the neutron for the atom is 12
but for the isotope why is it 12 as well, i thought isotopes have
diff number of neutrons?