Moles conversion

Sometimes chemists have to analyze substances about which they know very little. A chemist may isolate an interesting molecule from a natural source, such as a plant or an insect. Under these conditions the chemical formula must be deduced from mass percentage data, without the help of an expected formula. A four-step procedure accomplishes this by using mass-mole conversions, the molar masses of the elements, and the fact that a chemical formula must contain integral numbers of atoms of each element. 

Because moles are the currency of chemistry, all stoichiometric computations require amounts in moles. In the real world, we measure mass, volume, temperature, and pressure. With the ideal gas equation, our catalog of relationships for mole conversion is complete. Table lists three equations, each of which applies to a particular category of chemical substances. 

The chemical structures of I and VI reveal the strong similarities between ethanoic and methanoic acids, yet the smaller molecule is considerably nastier to the skin. Why Methanoic acid dissociates in water to form the solvated methanoate anion HCOO-(aq) and a solvated proton in a directly analogous fashion to ethanoic acid dissolving in water Equation (6.1). In methanoic acid of concentration 0.01 mol dm-3, about 0.14 per cent of the molecules have dissociated to yield a solvated proton. By contrast, in ethanoic acid of the same concentration, only 0.04 per cent of the molecules have dissociated. We say the methanoic acid is a stronger acid than ethanoic since it yields more protons per mole. Conversely, ethanoic acid is weaker. 

The basic calculations fall into two categories. Simple calculations, such as the change in temperature or the change in volume, are the easiest to forget. Simple calculations may also include mass-to-mole conversions. The other calculations normally involve entering values into one of the equations given at the beginning of the previous chapters of this book. 

For many mole conversions, you need to look up atomic masses on the periodic table (see Chapter 4). The atomic masses you see in different periodic tables may vary slightly, so for consistency, we ve rounded all atomic mass values to two decimal places before plugging them into the equations. We round answers according to significant figure rules (see Chapter 1 for details). 

See the earlier section Doing Mass and Volume Mole Conversions. ... 

For every mole of nitrogen reactant, a chemist expects 2 moles of ammonia product. Similarly, for every 3 moles of hydrogen reactant, the chemist expects 2 moles of ammonia product. These expectations are based on the coefficients of the balanced equation and are expressed as mole-mole conversion factors as shown in Figure 9-1. 

If you look at Figure 9-2, you can see that it isn t possible to convert directly between the mass of one substance and the mass of another substance. You must convert to moles and then use the mole-mole conversion factor before converting to the mass of a new substance. The same can be said for conversions from the particles or volume of one substance to that of another substance. The mole is always the intermediary you use for the conversion. 

Notice how both calculations require you to first convert to moles and then perform a mole-mole conversion using stoichiometry from the reaction equation. Then you convert to the desired units. Both solutions consist of a chain of conversion factors, each factor bringing the units one step closer to those needed in the answer. 

Overall, samples 1-6 show that the reaction of dimethylamine with PMMA is facile, results in few side-products (MAA or amide) up to about 70 mole % conversion, and requires about 1 1 dimethylamine MMA stoichiometery. As conversion approaches the Flory limit (ca. 86 mole %), more acid (MAA) is seen, and finally at high excess amine levels and pressures, a significant amount of N,N -dimethyl methacrylamide is seen (sample 6). Other experiments at DMA/MMA ratios of 0.25-0.83 and DMA pressures of up to 4240 KPa did not produce any significant differences in anhydride or amide levels. The FTIR spectra are shown in Figure 1. Note that the anhydride has a coupled carbonyl stretch (asym=1802 cm 1, sym=1759 cm 1). This agrees well with previous literature (1800, 1760 cm 1)8 and (1800, 1758 cm 1).9... 

In a mass-to-mass calculation, convert the given mass to moles, apply the mole-to-mole conversion factor to obtain the moles required, and finally convert moles required to mass. 

The problem gives the mass of sucrose and asks for a mass-to-mole conversion. Use the molar mass of sucrose as a conversion factor, and set up an equation so that the unwanted unit cancels. 

First, find out how many moles of Cl2 are in 25.0 g of Cl2. This gram-to-mole conversion is done in the usual way, using the molar mass of Cl2 (70.9 g/mol) as the conversion factor ... 

To calculate the molarity of the KMn04 solution, we need to find the number of moles of KMn04 present in the 22.35 mL of solution used for titration. We do this by first calculating the number of moles of oxalic acid that react with the permanganate ion, using a gram-to-mole conversion with the molar mass of H2C2O4 as the conversion factor ... 

Because NaOH and Ca(OH)2 are strong bases, they are 100% dissociated and their [OH ] is directly related to their initial concentrations. To calculate the [OH ] in a solution prepared by dissolving CaO, we must first do a mass-to-mole conversion and then use the balanced equation for the reaction of CaO with water to find the number of moles of OH-in the solution. In each case, [H30 + ] = Kw/[OH-] and pH = — log[H30 + ]. 

From what you have learned about moles to this point, you can write six mole conversion factors. Remember that you can write two factors for each (one the reciprocal of the other). 

TVvo of the six mole conversion factors are shown below. Write the other four. 1 mole... 

Treatment of butadiene or 1,4-butanediol with hydrogen sulfide over an alumina catalyst, or an iron sulfide/alumina catalyst, leads to the formation of thiophene. This method has been more useful in the benzothiophene series. Styrene with four equivalents of hydrogen sulfide, when passed over an iron sulfide/aluminum oxide catalyst at 600 °C for 20 seconds, gave a 60% mole conversion to benzo[6]thiophene (47JA2008). Similar treatment of ethylbenzene over a chromium oxide-alumina catalyst gave an 18% yield of benzo[6]thiophene, accompanied by the evolution of hydrogen (48JA2495). 

We know the rate, but we still need to determine the number of nuclei present at time t (we only know the mass of the sample). To do this, we will need to determine how many technetium-99 atoms are present in 1.0 X 10 3 g of the substance). This is a mole-conversion problem (see Chapter 12) ... 

The most basic mole calculation is the mole-to-mass (or mass-to-mole) conversion. It is simply a matter of using dimensional analysis and the molar mass of the substance to make the conversion. 

The correct answer is (B). First you have to balance the equation 2A1 + 6HC1 — 2A1C13 + 3H2. Now this becomes a very simple mole-to-mole conversion ... 

The same basic formulas for mole conversion with one substance are used to compare two substances in a chemical reaction. The only difference is that one substance must be converted to another using the mole ratio before the calculation can be completed. 

The correct answer is (B). This is a mole-to-mole conversion. If you have a balanced equation to start, you can solve these in your head. The mole ratios from the balanced equation allow you to quickly convert between moles of substances. The ratio of Cl2 to SiCl4 is 2 to 1. That means you will produce only half as many moles of SiCl4, or 1.92 mol. You can also solve the problem using a formula, as shown below ... 

TABLE 5.2 Seven Liquid Hourly Space Velocity/Mole % Conversion Data Pairs 1... 

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