1. D.
2. B.
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1. Not a reliable or accurate way to measure rate of reaction.
HCl is in excess. If it is present in large excess, its molarity
will hardly change throughout the reaction.
2. Unlike other metal parts of the car which are painted to
prevent rusting (by preventing direct contact between water and the
iron), the exhaust pipe is usually unpainted. The second reason is
that it is usually warmer than other metallic parts of the car,
because it acts as a channel for hot waste gases. The
higher the temperature, the faster the rate of corrosion.
3. Bubbles of gas generated around the zinc solid. This is
because protons from the acid are being reduced to hydrogen gas,
while the zinc atoms are oxidized to Zn2+ ions. The other
observation, is that the size of the zinc metal becomes smaller
over time, as it dissolves into the acid. This is because zinc
metal is a solid, but reacts with the acid to form soluble Zn2+
ions.
4. The reaction will involve vigorous efferverscence, and hence
some acidic splatter will result. The cotton wool helps to prevent
the acid splatter from reaching the U-tube, allowing only carbon
dioxide gas generated to pass into the gas syringe.
on o lvl topic: energy changes
1) formation of hcl from hydrogen n chlorine is a strongly
exothermic rnx. from tis, it can be deduced that
a)the temp falls during rxn
b)heat is absorbed in the rnx
c)hcl gas burns readily in air OR
d)hcl is not easily decomposed by heat
2)when hydrogen n iodine combine to form hcl, heat is absorbed.
from this, we can deduce that
a) hydrogen n iodine react more rapidly at lower temps
b)the energy involved in making bonds is less than that involved
in breaking bonds
c)more bonds are broken than formed OR
d)formation of hydrogen iodide uses up energy
o lvl topic: speed of rnx
1) an experiment is carried out involving magnesium ribbon and
excess dilute hcl. vol of h2 is measured to find rate of rxn. Qn:
can the change in the concentration of hcl be used to measure the
rate of this reaction too? explain why.
2)give too reasons why the exhaust pipe of a car rusts more
rapidly than the other metal parts of the car
3)zinc reacts wif an excess of dilute h2so4. describe two
changes that you would observe during the rxn
4) a conical flask containing mgco3 and hcl is allowed to react,
den the flask is connected to a u tube containing cotton wool b4
the hydrogen gas is allowed to be collected in a gas syringe.
explain the purpose of using the cotton wool in the setup.
