There are a few questions that I needed to be answered for my chemestry class ASAP!! Thanks!!!?

Question

When potassium cyanide (KCN) reacts with acids, a deadly poisonous gas, hydrogen cyanide (HCN), is given off. Here is the equation below.

KCN(aq) + HCl(aq) KCl(aq) + HCN(g)
If a sample of 0.230 g of KCN is treated with an excess of HCl, calculate the amount of HCN formed, in grams.

Nitric oxide (NO) reacts instantly with oxygen gas to form nitrogen dioxide (NO2), a dark-brown gas.

2 NO(g) + O2(g) 2 NO2(g)
In one experiment 0.675 mole of NO is mixed with 0.378 mole of O2.
Calculate the number of moles of NO2 produced.

Consider the reaction below.

MnO2 + 4 HCl MnCl2 + Cl2 + 2 H2O
How many grams of Cl2 will be produced?

Titanium(IV) oxide (TiO2) is a white substance produced by the action of sulfuric acid on the mineral ilmenite (FeTiO3).

FeTiO3 + H2SO4 TiO2 + FeSO4 + H2O
It is opaque and its nontoxic properties make it suitable as a pigment in plastics and paints. In one process 9.90 103 kg of FeTiO3 yielded 1.80 103 kg of TiO2. What is the percent yield of the reaction?

Answer 1

Moles(KCN) = 0.23g/ 65 (MrKCN) = 0.003538 mole
From the eq'n 1 mole KCN produces 1 mole HCN
therefore 0.003538 molKCN produces 0.003538 mol HCN
Mass(HCN)= 0.003538 x 27 = 0.09554 g

2 mole (NO) react with 1 mole (O2)
0.675 mole(NO) react with 0.3375 moles(O2)
Hence oxygen is in excess.
So 0.675 moles NO2 produced.
Because molar ratios are
2:1::2

For MnO2 + 4HCl reaction need as mass of starting material.

Moles FeTiO3 = 9.90/152 = 0.06513 moles
MolesTiO2 = 0.06513 (As molar ratios are 1:1)
Mass TiO2 = 0.06513 x 80 = 5.2105g (Theoretical 100% yield).

1.80/5.2105 x 100 = 34.54% yield!!!

Answer 2

Most of your questions are stoichiometry problems. Since they can be asked in a zillion different ways, it's important for you to understand HOW you work them, not to just know how to get the right answer.

So, for your first one, you have a balanced equation (absolutely essential) and are given a mass of one reactant and asked to determine the mass of the product formed. Notice that in the balanced equation, both of those compounds have a coefficient of 1. The basic process is to convert grams of KCN to moles KCN using the molecular weight. Then using the coefficients of the substances from the balanced equation, convert moles KCN into moles HCN. Finally convert moles HCN into grams, again using ITS molecular weight.. So, for this problem:

(0.230 g KCN) / 65.1 g/mol = 0.00353 mol KCN

0.00353 mol KCN ( 1 mol HCN/1 mol KCN) = 0.00353 mol HCN

0.00353 mol HCN ( 27.0 g/mol) = 0.0954 grams HCN

The rest of your problems will be worked in a comparable manner. In the second step, the ratio between moles HCN and KCN was 1:1. In other questions it will be different. The ratio is gotten from the balanced equation.

Now, in your last problem, work the problem this way starting with your FeTiO3 and calculate the mass of TiO2 that you could possibly make. Then, you can calculate the % yield by dividing the mass that was obtained by the mass the could have been gotten (the theoretical yield) and multiplying by 100.

Hope this helps. If you need additional help, message me...

Answer 3

The first and second one are almost the same, so just use the same procedure:
grams --> moles --> mole ratio --> moles --> grams

Example:
0.230g KCN x 1 mol KCN x 1 mol HCN x 27 g HCN = gHCN
------------------ -------------- --------------- ---------------
------------------ 61.5 g 1 mol KCN 1 mol HCN

For the second one, just go from moles to mole ratio to moles for both of the reactants. The smaller number will be the number of moles of NO2 produced.

For the %yield one:

amt of actual yield produced
---------------------------------------- = % yield
theoretical yield
(use the same methods as for the previous ones to find the theoretical yield)