Chemical formulas calculation

Determining Chemical Formulas Calculations in Chemical Reactions Limiting Reactants... 

Mineral Chemical formula Calculated SolubiUty (mol/1) Experimental... 

In lesson B the student has to recognize the information contained in a chemical formula, calculate the formula weight from the chemical formula, and determine the molecular formula and molecular weight. 

To this point, our study of chemistry has been largely qualitative, involving very few calculations. However, chemistry is a quantitative science. Atoms of elements differ from one another not only in composition (number of protons, electrons, neutrons), but also in mass. Chemical formulas of compounds tell us not only the atom ratios in which elements are present but also the mass ratios. 

Turquoise has the following chemical formula CuAl (P04)4(0H)8 4H20. Calculate the mass percent of each element in turquoise. 

Calculate the molar mass of a compound, given its chemical formula. 

Cyclohexane (C) and methylcyclopentane (M) are isomers with the chemical formula C6H12. The equilibrium constant for the rearrangement C M in solution is 0.140 at 25°C. (a) A solution of 0.0200 mol-L 1 cyclohexane and 0.100 mol-I. 1 methylcyclopentane is prepared. Is the system at equilibrium If not, will it will form more reactants or more products (b) What are the concentrations of cyclohexane and methylcyclohexane at equilibrium (c) If the temperature is raised to 50.°C, the concentration of cyclohexane becomes 0.100 mol-L 1 when equilibrium is reestablished. Calculate the new equilibrium constant, (d) Is the reaction exothermic or endothermic at 25°C Explain your conclusion. 

STRATEGY When Ba(OH)2 dissolves in water, it provides OH ions most hydroxides of Groups 1 and 2 can be treated as fully dissociated in solution. Decide from the chemical formula how many OH ions are provided by each formula unit and calculate the concentrations of these ions in the solution. To find the concentration of H,Oj ions, use the water autoprotolysis constant Kw = [H,0 1 [OH ]. 

Sei f-Test 10.6A Write the chemical formula for the conjugate acid of the base pyridine, C4H4N, and calculate its pK,. 

As chemical formulas become more complicated, the calculation of molar mass requires more steps, as shown in Examples 3-10 and 3-11. 

The line structure demonstrates how the atoms are connected in the molecule, but we do not need this information because the chemical formula is provided. We use the chemical formula to calculate the... 

Before we can calculate a molar mass, we need a chemical formula. Then we can calculate the masses of each of the elements in one mole of the compound. 

Mass-mole-number calculations often involve atoms yvithin a compound as well as the compound itself. The chemical formula provides the link between moles of a compound and the number of moles of the compound s individual elements ... 

The chemical formula of a compound contains essential information about its composition. The formula identifies which elements are present, and it states the number of atoms of each kind present in one unit of the compound. We need the chemical formula of a substance to calculate its molar mass. In fact, almost all chemical calculations require the correct chemical formula. How are chemical formulas determined in the first place ... 

The elemental analysis of a compound is usually determined by a laboratory that specializes in this technique. A chemist who has prepared a new compound sends a sample to the laboratory for analysis. The laboratory charges a fee that depends on the type and number of elements analyzed. The results are returned to the chemist as a listing of mass percent composition. The chemist must then figure out which chemical formula matches this composition. If a chemist has reason to expect a particular chemical formula, the observed percentages can be matched against the calculated percentages for the expected formula. This process is illustrated in Example 3-13. 

As with all calculations of chemical amounts, we must work with moles. Because grams are asked for, we must do a mole-mass conversion this requires the molar mass of the substance, which in turn requires that we know the chemical formula. 

C03-0105. The line stmctures of three different plant growth hormones are given below. For each one, write the chemical formula for the compound and calculate its molar mass. 

Does it bother you to find that neither the chemical formula nor the molar mass is needed for these calculations Remember that not all data are necessarily required for any particular calculation. Because average kinetic energy depends on temperature but not on molar mass, we do not need mass information to do this problem. 

We can use the ideal gas equation to calculate the molar mass. Then we can use the molar mass to identify the correct molecular formula among a group of possible candidates, knowing that the products must contain the same elements as the reactants. The problem involves a chemical reaction, so we must make a connection between the gas measurements and the chemistry that takes place. Because the reactants and one product are known, we can write a partial equation that describes the chemical reaction CaC2(. ) +H2 0(/) Gas -I- OH" ((2 q) In any chemical reaction, atoms must be conserved, so the gas molecules can contain only H, O, C, and/or Ca atoms. To determine the chemical formula of the gas, we must find the combination of these elements that gives the observed molar mass. 

C12-0063. Urea, a fertilizer, has the chemical formula (NH2)2 CO. Calculate the vapor pressure of water above a fertilizer solution containing 7.50 g of urea in 15.0 mL of water (density = l.OOg/mL), at a temperature for which the vapor pressure of pure water is 33.00 torr. 

C12-0064. Ethylene glycol, an automobile coolant, has the chemical formula HOCH2 CH2 OH. Calculate the vapor pressure of water above a coolant solution containing 65.0 g of ethylene glycol dissolved in 0.500 L of water (density = 1.00 g/mL), at 100 °C, the boiling point of pure water. 

Once the composition of the aqueous solution phase has been determined, the activity of an electrolyte having the same chemical formula as the assumed precipitate can be calculated (11,12). This calculation may utilize either mean ionic activity coefficients and total concentrations of the ions in the electrolyte, or single-ion activity coefficients and free-species concentrations of the ions in the electrolyte (11). If the latter approach is used, the computed electrolyte activity is termed an ion-activity product (12). Regardless of which approach is adopted, the calculated electrolyte activity is compared to the solubility product constant of the assumed precipitate as a test for the existence of the solid phase. If the calculated ion-activity product is smaller than the candidate solubility product constant, the corresponding solid phase is concluded not to have formed in the time period of the solubility measurements. Ihis judgment must be tempered, of course, in light of the precision with which both electrolyte activities and solubility product constants can be determined (12). 

In the problems above, the percentage data was calculated from the chemical formula, but the empirical formula can be determined if the percent compositions of the various elements are known. The empirical formula tells us what elements are present in the compound and the simplest whole-number ratio of elements. The data may be in terms of percentage, or mass, or even moles. But the procedure is still the same convert each to moles, divide each by the smallest number, then use an appropriate multiplier if needed. The empirical formula mass can then be calculated. If the actual molecular mass is known, dividing the molecular mass by the empirical formula mass gives an integer (rounded if needed) that is used to multiply each of the subscripts in the empirical formula. This gives the molecular (actual) formula, which tells which elements are in the compound and the actual number of each. 

Common crystal-chemical formulae. Unit cell volumes and interatomic distances. In the analysis and description of a structure some calculation may be useful. A few common formulae are collected here. 

In terms of the visual clarity of its presentation, biochemistry has still to catch up with anatomy and physiology. In this book, we sometimes use simplified ball-and-stick models instead of the classical chemical formulae. In addition, a number of compounds are represented by space-filling models. In these cases, we have tried to be as realistic as possible. The models of small molecules are based on conformations calculated by computer-based molecular modeling. In illustrating macromolecules, we used structural infor-... 

For nonmolecular substances like sodium chloride, the use of the word mole, with its connotation of molecules, is inappropriate. A comparable unit, the gram formula weight, is used it is defined as the sum in grams of the atomic weights of all the atoms in the chemical formula of the substance. For sodium chloride (NaCl), one gram formula weight is calculated as... 

Occasionally, you may be asked to calculate the mole fraction of a solution, which is the ratio of the number of moles of either solute or solvent in a solution to the total number of moles of solute and solvent in the solution. By the time chemists defined this quantity, however, they had finally acknowledged that they had too many m variables, and they gave it the variable X. Of course, chemists still need to distinguish between the mole fractions of the solute and the solvent, which unfortunately both start with the letter s. To avoid further confusion, they decided to abbreviate solute and solvent as A and B, respectively, in the general formula, although in practice, the chemical formulas of the solute and solvent eire usually written as subscripts in place of A and B. For example, the mole fraction of sodium chloride in a solution would be written as... 

A chemical formula tells the numbers and the kinds of atoms that make up a molecule of a compound. Because each atom is an entity with a characteristic mass, a formula also provides a means for computing the relative weights of each kind of atom in a compound. Calculations based on the numbers and masses of atoms in a compound, or the numbers and masses of molecules participating in a reaction, are designated stoichiometric calculations. These weight relationships are important because, although we may think of atoms and molecules in terms of their interactions as structural units, we often must deal with them in the lab in terms of their masses—with the analytical balance. In this chapter, we consider the Stoichiometry of chemical formulas. In following chapters, we look at the stoichiometric relations involved in reactions and in solutions. 

Hardness measured in units of Mohs scale Mineral Chemical formula Measured 1 Vickers Hv (with micro- measurement) lardness Rnoop hk. - H0 in nl >0 i Khrushchev tr° yC° hardness efficient. 1f classes A h = Ho Hl = 0.7 /Hv Htheor calculated by Pova-rennykh (1963) Optimum load of indenter P, mN ... 

Hardness measured in units of Mohs scale Chemical formula Measured hardness Aniso- H0 in Khrushchev hardness classes Ho = 0.7 pHy H theor calculated by Pova-rennykh (1963)... 

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