To determine the mass in grams of of nickel, we first need to convert atoms to moles. To do this we need to know that . Then we will convert moles to grams using the atomic mass of nickel, which can be found on the periodic table. The atomic mass of  is . 

Now we have all of the information we need to perform the conversion:

The conversion of grams to atoms is a two-step process. First, we need to convert grams to moles using the molecular mass of sulfur. The molecular mass of sulfur can be found on the periodic table and is equal to 

Then we will convert moles to atoms using our knowledge that . Using all this information we will perform the following conversion:

In a chemical reaction, the limiting reactant determines how much product can be created. Given two reactants in different quantities, the limiting reactant is defined as the reactants that cannot fully convert the given amount of the other reactant to product.

The mass, number of moles, volume, and partial pressure of the reactants can help to identify the limiting reagent, but cannot be used without a given chemical equation with molar ratios. For example, imagine that fifty moles of reactant A are needed to react two moles of reactant B. You are given 49 moles of reactant A and 2 moles of reactant B. Even though you have more mass, volume, and moles of reactant A, it is still the limiting reactant because it cannot fully convert reactant B to the product.

In order to determine the limiting reactant, we can use a calculation to determine how much of one reactant is needed in order to use up the other. For example, we can see how much hydrogen gas is necessary in order to use up all  of nitrogen gas that we have:

In other words, we need  of hydrogen gas in order to use up  of nitrogen gas. Since we have  of hydrogen gas, we have more than enough to react all of the nitrogen gas, and the nitrogen gas will be used up before the hydrogen gas. As a result, nitrogen gas is the limiting reactant.

Limiting reactants are determined when there is an excess of a particular reactant, in relation to the other reactants available. When reactants are compared, one must always compare the molar ratio in order to determine which reactant is limited. In this reaction, if we are given the available amount of each reactant, we will need to convert the given amount of one reactant (A) to the necessary amount of the other (B) required to fully react. If we find that reactant A is available in excess, then reactant B will be the limiting reagent. The only way to compare these two terms, however, is by using the molar ratio in the reaction.

Let's begin by converting our reactants from grams to moles. Note that both gases are diatomic, meaning that there are two atoms per molecule.

Molecular weights:

Conversion to moles:

We have 2 moles of oxygen gas and 3 moles of hydrogen gas. Next, look at the given reaction:

Two moles of hydrogen gas are consumed to react each mole of oxygen gas. We can use this ratio to find the number of moles of oxygen gas needed to react all of the hydrogen given in this question.

Only 1.5 moles of oxygen gas are needed to react all of the hydrogen gas. Since we have 2 moles of oxygen gas, some of it will remain unreacted when all of the hydrogen gas has been used. This means the hydrogen gas is the limiting reagent.

Find the amount of unreacted oxygen gas:

Convert to grams:

First, we must determine how many moles of each reactant begin the reaction by multiplying the molarity by the volume. Don't forget to convert volume to liters!

Next, use the reaction coefficients (i.e. the stoichiometry) to determine how many moles of calcium carbonate could be formed from each of the reactants. In this case, there is a 1:1 molar ratio between both reactants and calcium carbonate.

Thus, 0.0125 moles of potassium carbonate could form 0.0125 moles of calcium carbonate, while 0.0175 moles of calcium nitrate could form 0.0175 moles of calcium carbonate. The maximum amount of product is going to be determined by the limiting reactant, i.e. the reactant that provides the least amount of product. In this case, the limiting reactant is potassium carbonate, and the maximum yield of calcium carbonate is 0.0125mol.

For the final step convert this value to grams:

First, we must determine how many moles of each reactant begin the reaction by multiplying the molarity by the volume. Don't forget to convert volume to liters!

Next, use the reaction coefficients (i.e. the stoichiometry) to determine how many moles of calcium carbonate could be formed from each of the reactants. In this case, there is a 1:1 molar ratio between both reactants and calcium carbonate.

Thus, 0.0125 moles of potassium carbonate could form 0.0125 moles of calcium carbonate, while 0.0175 moles of calcium nitrate could form 0.0175 moles of calcium carbonate. The maximum amount of product is going to be determined by the limiting reactant, i.e. the reactant that provides the least amount of product. In this case, the limiting reactant is potassium carbonate, and the maximum yield of calcium carbonate is 0.0125mol.

For the final step convert this value to grams:

The remaining mass with be equal to the mass of the sodium chloride in the solution. Once the solvent (water) evaporates, the solute will remain.

Atomic mass of sodium is ~23. Atomic mass of chlorine is ~35.5. Molecular mass of NaCl is ~58.5.

This question is asking us to solve for molality, which has the following equation:

Note how the equation does not ask for liters of solution like molarity, but instead requires the kilograms of solvent used in the solution. By dividing the mass of the sodium chloride by its molar mass, we can solve for the moles of sodium chloride in solution.

This will allow us to solve for the mass of water used in the solution.

This gives us the mass of water required to make the solution.