Percentage by mass

In a dry powder the percentage of each constituent in a mixture is calculated in grams as expressed as a proportion of the total mass of 100 g of the sample 100 g of a mixture containing 30 g of substance A and 70 g of B would have a percentage composition of 30 % A and 70 % B. 

If a solution is very dilute, the mass of the active materials in water solution can also be expressed as a percentage because the mass of the materials present is negligible compared with the mass of the water. 

We appreciate that the figures in this chapter are mind-bending, but it is essential that correct values are understood when prescribing quantities for patients. It might be useful to make a single sheet of the most used units and keep them handy for reference. 

How many grams of glucose (C6Ht206), C= 12, H= 1, 0=16, Molar mass = 180) will it take to make the following solutions  

How many grams of material will be needed to make up the following solutions  

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Trichloroethane, Cj Cl is the active ingredient in aerosols that claim to stain-proof men s ties. Trichloroethane has a vapor pressure of 100.0 mm Hg at 20.0°C and boils at 74.1°G An uncovered cup (y pint) of trichloroethane (d = 1325 g/mL) is kept in an 18-ft3 refrigerator at 39°F. What percentage (by mass) of the trichloroethane is left as a liquid when equilibrium is established ... 

Of the polymers referred to in Table 23.1 which one contains the highest percentage by mass of carbon ... 

In [324] it was noted that in case of polyethylene-based PFCM it is the MM which is the parameter controlling the composite viscosity. For a fixed MM, the viscosity of the melt increases symbatically with the filling percentage by mass. The nature of the viscosity versus MM relationship is similar for both PFCM and mechanical mixtures, that is, in terms of rheology the two systems are practically identical. 

F.20 Dolomite is a mixed carbonate of calcium and magnesium. Calcium and magnesium carbonates both decompose on heating to produce the metal oxides (MgO and CaO) and carbon dioxide (C02). If 4.84 g of residue consisting of MgO and CaO remains when 9.66 g of dolomite is heated until decomposition is complete, what percentage by mass of the original sample was MgC03 ... 

F.23 A mixture of NaN03 and Na2S04 of mass 5.37 g contains 1.61 g of sodium. What is the percentage by mass of NaNO. in the mixture ... 

A 1.40-g sample containing radioactive cobalt was kept for 2.50 a, at which time it was found to contain 0.266 g of 67Co. The half-life of 67Co is 5.27 a. What percentage (by mass) of the original sample was f,Co ... 

The mass percent composition is a listing of the mass of each element present in 100 g of a compound. This percentage by mass listing is also called the compound s elemental analysis. 

C03-0087. A chemical compound was found to contain only Fe, C, and H. When 5.00 g of this compound was completely burned in O2, 11.8 g of CO2 and 2.42 g of H2 O were produced. Find the percentage by mass of each element in the original compound and its empirical formula. 

C04-0159. Bronze is an alloy of copper and zinc. When a 5.73-g sample of bronze was treated with excess aqueous HCl, 21.3 mg of H2 was produced. What was the percentage by mass composition of the bronze ... 

The HLB of a relatively pure poly(oxyethylene) adduct can be calculated from theoretical data [37]. For these agents the HLB is an indication of percentage by mass of the hydrophilic portion, divided by five to give a conveniently small number. For example, if the hydrophilic portion of a purely hypothetical nonionic agent accounted for 100% of the molecule (such a product cannot, of course, exist), its HLB is 20. Similarly, a more plausible product in which 85% of the molecule is accounted for by the hydrophilic portion has an HLB of 85/5 = 17. The ICI Americas Inc. method of calculating the theoretical HLB of a sorbitan monolaurate nonionic having 20 oxyethylene units per molecule is given in... 

Ammonium nitrate, e.g. ICI s NITRAM , is very widely used because of its high percentage by mass of nitrogen. 

Calculate the overall efficiency of the collector and the percentage by mass of the emitted dust that is smaller than 20 im in diameter. If the dust burden is 18 g/m3 at entry and the gas flow is 0.3 m3/s, calculate the mass flow of dust emitted. 

The percentage by mass of dissolved and undissolved solids in the final product = (0.25 x 75) + 25 = 43.8 per cent and hence the mass balance becomes ... 

What was the percentage, by mass, of the water in the hydrate based upon this experiment ... 

Sometimes elemental microanalysis results are given as percentages by mass. The process used to calculate the empirical formula from the percentage by mass is similar to that just shown, assuming the total mass of the sample to be 100 g. 

The next four pages will look at techniques that can be used together as part of one experiment. To illustrate this, we will consider an experiment to determine the percentage by mass of manganese in a steel paper clip using colorimetry. 

In an experiment to determine the percentage by mass of manganese in a steel paper clip, it is necessary to prepare various concentrations of standard potassium permanganate solutions. You will learn more about this experiment on p. 88. A standard 0 0010 mol h solution of potassium permanganate is often used as a stock solution in this experiment. Dilutions of the stock solution are prepared by accurately transferring a known volume of the stock solution, using a pipette or a burette, into a volumetric flask (standard flask). The flask is then carefully filled to the graduation mark with deionised water. 

Calculate the percentage by mass of manganese in the steel paper clip. 

Figure 12.1 Abundances of the first 40 elements as a percentage by mass of Earth s crust (filled squares) and in the solar system (open circles). Data from the CRC Handbook of Chemistry and Physics, 75th ed., 1994. (Figure also appears in color figure section.)...

Sometimes the composition of a compound is given as a percentage by mass of the elements present. In cases such as this the procedure shown in the next example is followed. 

Sometimes it is necessary to work out the percentage, by mass, of water of crystallisation in a hydrated salt. The method is the same as that used in Chapter 4, p. 65, but this time the H20 is treated as an element in the calculation. 

The table below shows the percentage by mass of some of these different fractions in petroleum. Also shown is the demand for each fraction expressed as a percentage. 

The percent composition of a substance is the percentage by mass of each element. Chemical composition is used to verify the purity of a compound in the lab. An impurity will make the actual composition vary from the expected one. 

This next type of problem occurs quite frequently on the AP test. This calculation is the stepping-stone toward determining the empirical or molecular formula for a compound. The procedure allows you to determine the percentage by mass that a given substance exists in a compound or what percentage of a compound is composed of a particular substance. In the procedure, you need to determine the mass percentage of each element that is in the compound. You do so with the following calculation ... 

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