Question

Q1: Convert 23.5 g Ti to moles Q2: We need 0.254 moles of Iron (III) chloride for an experiment. How many grams do we need to weigh? Q3: Tungsten wire is the filament inside most old­style incandescent light bulbs. In a typical light bulb, the tungsten filament weighs 0.635 grams. How many atoms of tungsten are there in such a light bulb filament? Q4:Calcium phosphate is widely found in nature in the form of natural minerals. Is is also found in bones and some kidney stones. In one case a sample is found to contain 0.864 moles of phosphorus. How many moles of Ca3 (PO4 )2 are in that sample? Q5: Chlorophyll, the green pigment in leaves, has the formula C55H72MgN4O5 . If 0.0011 g of Mg is available to a plant for chlorophyll synthesis, how many grams of carbon will be required to completely use up the magnesium? Q6: A sample of liquid with mass of 8.657 g was decomposed into its elements and gave 5.217 g carbon, 0.9620 g hydrogen, and 2.478 g of oxygen. What is the percentage composition of this compound? Q7: 2.57 g of sample if a compound is composed of only tin and chlorine was found to contain 1.17 g tin. What is the compound’s empirical formula?

Answer 1

1.

23.5 g Ti = 23.5/ 183.84

2.

0.254 moles of Iron (III) chloride = 0.254 * 162.2

3.

0.635 grams = 0.635 grams *N_{A =} 0.635 grams * 6.023 * 10^23

4.

Ca3 (PO4 )2 ---> 3Ca⁺² + 2 PO₄^-2

Hence moles of Ca3 (PO4 )2 = 0.864/2

5.

0.0011 g Mg ? ? g C

0.0011 g Mg -> mol Mg -> mol C -> g C

24.3050 g Mg = 1 mol Mg

1 mol Mg ? 55 mol C

1 mol C = 12.011 g C

6.

7.

118.7g Sn= 1 mol Sn; 35,45g Cl= 1 mol Cl
mass of Sn= 1.17g Sn; mass of Cl= 2.57g-1.17g= 1.40g Cl
1.17g Sn (1 mol Sn/ 118.7g Sn)= 0.00986 mol Sn
1.40 g Cl (1 mol Cl/35.45g Cl)= 0.0395 mol Cl

(0.00986/0.00986)= Sn????; (0.0395/0.00986)= Cl????

Empirical formula = SnCl₄