3 Solution Questions Help!?!?

Question

1. What quantity represents the ratio of the nunmber of moles of solute for a given volume of solution?
2. We dissolve 5.00 grams of sugar, C12 H22 O11, in water to make 1.000 L of solution. What is the concentration of this solution expressed as a molarity?
3. You evaporate all of the water from 100. mL of NaCl solution and obtain 11.3 grams of NaCl. What was the molarity of the NaCl solution?

Answer 1

1. molar or m.

2. the formula of getting the molarity is (moles of given substance) divided by (volume of solution in Liters)

so to get the moles of sugar, we have to get first the atomic weight of each substance.

C = 12; H = 1; O = 16.

Since there are 12 Cs, we multiply 12(12) = 144 g/mol.

then

22 Hs; 22(1) = 22 g/mol

11 Os; 11(16) = 176 g/mol

then add 144 + 22 + 176 = 342 g/mol

so 5 grams of sugar * 1 mol/342g

we have to cancel the grams.

so there is 0.1461988 mol

so since there is 1 L of solution looking back at the formula

molarity = moles of substance/L of solution

the answer here is

0.1461988 mol/L.

how many decimal places do u need anyway. just divide 5 by 342 and voila.

3. 11.3 grams * 1 mol/58 grams = 0.1948275 mol

convert 100 mL into L.

100 mL * 1 L/1000mL = .1 L

so 0.1948275....mol / .1 L = 1.948275862 mol/L

Answer 2

1 molar is equal to a mole of solute dissolved to make a liter of solution.

Calculate the molar mass of the sugar. Divide 5.00 g by this number and you have moles of sugar. Since it is in 1 liter, it is also the molarity of the solution.

In you r last question, do the same. Calculate the molar mass of NaCl. Divide 11.3 g by this number and you have moles of Nacl. But it was dissolved in only 100 ml of solution. So multiply the moles by 10 and you have the molarity.