Balanced chemical equations, ratios from

To determine the concentration of a solute in a solution (e.g., HCl) we treat the unknown solution with a solution of known concentration and volume (e.g., NaOH) until the mole ratio is exactly what is required by the balanced chemical equation. Then from the known volumes of both solutions, the unknown concentration of the... 

Step 2 Use the mole ratio derived from the stoichiometric coefficients in the balanced chemical equation to convert from the amount of one substance (A) into the amount in moles of the other substance (B). For aA - / B or aA + hY> — cC, use... 

To summarize, the amounts of different reagents that participate in a chemical reaction are related through the stoichiometric coefficients in the balanced chemical equation. To convert from moles of one reagent to moles of any other reagent, multiply by the stoichiometric ratio that leads to proper cancellation of units ... 

You are starting with moles of iron and want grams of Fe203 so we ll first convert from moles of iron to moles of Fe203 using the ratio of moles of Fe203 to moles of iron as defined by the balanced chemical equation ... 

The ratio of 2 mol Fe203 to 4 mol Fe is called a stoichiometric ratio, which comes from the balanced chemical equation. 

Notice that this new stoichiometric ratio came from the balanced chemical equation. 

The mole is the most important concept in this chapter. Nearly every problem associated with this material requires moles in at least one of the steps. You should get into the habit of automatically looking for moles. There are several ways of finding the moles of a substance. You may determine the moles of a substance from a balanced chemical equation. You may determine moles from the mass and molecular weight of a substance. You may determine moles from the number of particles and Avogadro s number. You may find moles from the moles of another substance and a mole ratio. Later in this book, you will find even more ways to determine moles. In some cases, you will be finished when you find moles, in other cases, finding moles is only one of the steps in a longer problem. 

The term (2 mol HC1/1 mol H2) is a mole ratio. We got this mole ratio directly from the balanced chemical equation. The balanced chemical equation has a 2 in front of the HC1, thus we have the same number in front of the mol HC1. The balanced chemical equation has an understood 1 in front of the H2, for this reason the same value belongs in front of the mol H2. The values in the mole ratio are exact numbers, and, as such, do not affect the significant figures. 

To find the moles of IF5 from the limiting reagent, we need to use a mole ratio derived from information in the balanced chemical equation. (This is another place where, if we had not balanced the equation, we would be in trouble.)... 

You should be very careful when working problems involving gases and one or more other phases. The gas laws can only give direct information about gases. This is why there is a mole ratio conversion (from the balanced chemical equation) in this example to convert from the solid (KCI03) to the gas (02). 

Be able to convert from moles of one substance to moles of another, using the stoichiometric ratio derived from the balanced chemical equation. 

The pipeted volume is converted to moles by multiplying the liters of solution by its molarity. The moles of titrant are determined from the mole ratio in the balanced chemical equation for the reaction. The molarity of the solution is calculated by dividing the moles of titrant by the liters of titrant used. 

Convert the masses of the reactants and products to moles using their molar masses. Using the mole ratios from the balanced chemical equation, it is possible to determine how much material should react or be produced. These calculated values can be compared to the observed values. 

The balanced chemical equation for a reaction is used to set up the conversion factor from one substance to another and that conversion factor, the mole ratio for the reaction, is applied to the moles given to calculate the moles required. 

The most important step to all of these calculations is the use of a value known as the mole ratio. The mole ratio is the ratio of moles of one substance to moles of second substance. It is determined by the ratios of the coefficients from the balanced chemical equation. The mole ratio is used in all conversions since it allows you to switch from values that describe the given substances to values that describe the unknown substance. To facilitate this process, there is another chart, Figure 12.2, that provides guidelines for solving most problems. In this first type of calculation, we will use the mole ratio to convert from units of moles of the given substance to moles of the unknown substance. We re going to omit the states of the reactants and products so that you can focus your attention on the coefficients. 

It s fairly easy to conceptualize the idea of limiting reactants when you are given moles of the reactants. When you are given grams, it is not always so easy to see. When you have to solve limiting reactant problems, it is always necessary to determine the number of moles of each substance and compare that to the required ratios from the balanced chemical equation. Let s use the same reaction, but use masses instead of moles. 

The balanced chemical equation for this reaction shows that 1 mol of nitric acid reacts with 1 mol of sodium hydroxide. If equal molar quantities of nitric acid and sodium hydroxide are used, the result is a neutral (pH 7) aqueous solution of sodium nitrate. In fact, when any strong acid reacts with any strong base in the mole ratio from the balanced chemical equation, a neutral aqueous solution of a salt is formed. Reactions between acids and bases of different strengths usually do not result in neutral solutions. 

The coefficients in a balanced equation give the ratio of moles of each substance in the reaction to moles of any other substance. They also give the ratio of formula units of each substance to formula units of any other substance. The balanced chemical equation is the cornerstone from which we can calculate how much of one substance reacts with or is produced by a certain quantity of another substance (Chapter 10). 

Consider the reaction of phosphorus with chlorine as shown in the previous equation. Of course, the chemist is not required to place exactly 2 mol of P and 3 mol of CI2 in a reaction flask. The equation gives the reacting ratio. Ratios of coefficients from balanced chemical equations can be used as conversion factors for solving problems. 

It must be noted that the magnimdes of the quantities in the change due to reaction line are always in the ratio of the coefficients in the balanced chemical equation. It will also become apparent that the numbers of moles of reactants in the change line are subtracted from the initial quantities present and the numbers of moles of products are added to any initial quantities present. 

Step 4 Complete the change row by writing the number of moles of each substance that would react with or be produced from the quantity in step 3. Use a minus sign with each quantity of reactant. The magnitudes in the change row are in the same ratio as the coefficients in the balanced chemical equation. 

Convert the moles of H2SO4 to moles of (NH4)2S04, using the ratio from the balanced chemical equation. Convert the moles of (NH4)2S04 to mass of (NH4)2S04, using its molar mass. 

The number of millimoles of base is determined from the 2 1 ratio in the balanced chemical equation ... 

Use proportional reasoning to determine mole ratios from a balanced chemical equation. 

The coefficients in a balanced chemical equation show the relative numbers of moles of the substances in the reaction. As a result, you can use the coefficients in conversion factors called mole ratios. Mole ratios bridge the gap and can convert from moles of one substance to moles of another, as shown in Skills Toolkit 1. 

Substances are usually measured by mass or volume. As a result, before using the mole ratio you will often need to convert between the units for mass and volume and the unit mol Yet each stoichiometry problem has the step in which moles of one substance are converted into moles of a second substance using the mole ratio from the balanced chemical equation. Follow the steps in Skills Toolkit 2 to understand the process of solving stoichiometry problems. 

Convert the mass of Cu to moles, and then use the mole ratio of CuS04 Cu from the balanced chemical equation to determine the number of moles of CUSO4 needed. The moles of CUSO4 can be converted into volume of solution using the reciprocal of molarity. 1 mol Cu mol CUSO4 L solution mol Cu... 

You will write mole ratios from balanced chemical equations. 

You are given moles of the reactant propane, and moles of the product carbon dioxide must be found. The balanced chemical equation must be written. Conversion from moles of CgHg to moles of CO2 is required. The correct mole ratio has moles of unknown substance in the numerator and moles of known substance in the denominator. 

You are given the mass of the reactant and will need to write the balanced chemical equation. You then must convert from the mass of the reactant to moles of the reactant. You will next use a mole ratio to relate moles of the reactant to moles of the product. Finally, you will use the molar mass to convert from moles of the product to the mass of the product. 

Determine the moles of the unknown substance from the moles of the given substance. Use the appropriate mole ratio from the balanced chemical equation as the conversion factor. 

The next step involves determining whether the two reactants are in the correct mole ratio as given in the balanced chemical equation. The coefficients in the balanced chemical equation indicate that four moles of chlorine are needed to react with one mole of sulfur. This 4 1 ratio from the equation must be compared with the actual ratio of the moles of available reactants just calculated above. To determine the actual ratio of moles, divide the available moles of chlorine by the available moles of sulfur. 

Mole ratios are central to stoichiometric calculations. They are derived from the coefficients in a balanced chemical equation. To write mole ratios, the number of moles of each reactant and product is placed, in turn, in the numerator of the ratio with the moles of each other reactant and product placed in the denominator. 

To determine the hmiting reactant, the actual mole ratio of the available reactants must be compared with the ratio of the reactants obtained from the coefficients in the balanced chemical equation. 

From the balanced chemical equation, you know that 2 mol of butane reacts with 13 mol of oxygen, producing 8 mol of carbon dioxide and 10 mol of water vapor. By examining this balanced equation, you are able to find mole ratios of substances in this reaction. Avogadro s principle states that equal volumes of gases at the same temperature and pressure contain equal numbers of particles. Thus, when gases are involved, the coefficients in a balanced chemical equation represent not only molar amounts but also relative volumes. For example, if 2 L of butane reacts, the reaction involves 13 L of oxygen and produces 8 L of carbon dioxide and 10 L of water vapor. 

For volumes and concentrations that are commonly used in laboratory experiments, solving problems in terms of millimoles and milliliters often involves more convenient numbers than using moles and liters. We should note also that the reaction ratio that we obtain from any balanced chemical equation is exactly the same whether we express all quantities in moles or in millimoles. We will work many problems in this chapter using millimoles and milliliters. Let us see how we might solve Example 11-1 in these terms. 

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