Composition, percentage

Typical percentage compositions of light and heavy oils are given below. 

Rhenium hexafluoride is a cosdy (ca 3000/kg) material and is often used as a small percentage composite with tungsten or molybdenum. The addition of rhenium to tungsten metal improves the ductility and high temperature properties of metal films or parts (11). Tungsten—rhenium alloys produced by CVD processes exhibit higher superconducting transition temperatures than those alloys produced by arc-melt processes (12). 

X05, wt % P2O5 /H 0 Percentage composition in terms of the constituent polyphosphoric acids 7, n = High poly" d H4P4O, ... 

Type of waste Heating value, Btu/lb Percentage composition by weight Density, Ib/fF... 

If listed toxic chemicals are present equal to or above the de minimis cut-off level, your supplier must identify the specific components as they appear in Table II and provide their percentage composition by weight in the mixture or product, tf your supplier maintains that the identity ot a toxic chemical is a trade secret, a generic identity that is structurally descriptive must be supplied on the notice. A maximum concentration level must be provided if your supplier contends that chemical composition information is a trade secret. In either case, you do not need to make a trade secret claim on behalf of your supplier (unless you consider your use of the proprietary mixture a trade secret). On Form R, identify the toxic chemical you are reporting according to its generic name provided in the notification. (See the instructions for Part III, Section 2 on page 18 for more information.) tf the listed chemical is present below the de minimis level, no notification is required. 

Chemistry is a quantitative science. This means that a chemist wishes to know more than the qualitative fact that a reaction occurs. He must answer questions beginning How much. . . The quantities may be expressed in grams, volumes, concentrations, percentage composition, or a host of other practical units. Ultimately, however, the understanding of chemistry requires that amounts be related quantitatively to balanced chemical reactions. The study of the quantitative relationships implied by a chemical reaction is called stoichiometry. 

Prepare a mixture, by weight, of A with compound (IV). Inject a 0.3 pL sample of this mixture, measure the various peak areas and, after making appropriate corrections for differences in detector sensitivity, determine the percentage composition of A. 

Take some crude cresol mixture (1 g) and dissolve it in cyclohexane (20 mL). Obtain the infrared spectrum for the mixture if necessary, dilute the solution further with cyclohexane to obtain absorbances which will lie on the calibration graphs. From the selected absorption peaks calculate the absorbances for the three individual isomers and use the calibration graphs to calculate the percentage composition of the cresol mixture. 

Because the mass percentage composition is independent of the size of the sample— in the language of Section A, it is an intensive property—every sample of the substance has that same composition. A principal technique for determining the mass percentage composition of an unknown organic compound is combustion analysis. Chemists commonly send samples to a laboratory or agency for combustion analysis and receive the results as mass percentage composition (see Section M). 

If the chemical formula of a compound is already known, its mass percentage composition can be obtained from the formula. 

Mrzss percentage composition is found by calculating the fraction of the total mass contributed by each element present in a compound and expressing the fraction as a percentage. 

To convert the mass percentage composition obtained from a combustion analysis into an empirical formula, we must convert the mass percentages of each type of atom into the relative numbers of atoms. The simplest procedure is to imagine that we have a sample of mass 100 g exactly. That way, the mass percentage... 

EXAMPLE F.2 Sample exercise Determining the elemental composition from mass percentage composition... 

The mass percentage composition of a compound that assists in the coagulation of blood is 76.71 % C, 7.02% H, and 16.27% N. Determine the empirical formula of the compound. 

Self-TfsT F.4B The mass percentage composition of the compound thionyl difluoride is 18.59% O, 37.25% S, and 44.16% F. Calculate its empirical formula. 

The empirical formula of a compound is determined from the mass percentage composition and the molar masses of the elements present. 

F.l Citral is a fragrant component of lemon oil that is used in colognes. It has the molecular structure shown. Calculate the mass percentage composition of citral (black = C, gray = H, red = O). 

F.3 What is the mass percentage composition of I-carnitine, C7HhN03, a compound that is taken as a dietary supplement to reduce muscle fatigue ... 

F.14 Paclitaxel, which is extracted from the Pacific yew tree Taxus brevifolia, has antitumor activity for ovarian and breast cancer. It is sold under the trade name Taxol. On analysis, its mass percentage composition is 66.11% C, 6.02% H, and 1.64% N, with the balance being oxygen. What is the empirical formula of paclitaxel ... 

F.16 Cacodyl, which has an intolerable garlicky odor and is used in the manufacture of cacodylic acid, a cotton herbicide, has a mass percentage composition of 22.88% C, 5.76% H, and 71.36% As and a molar mass of 209.96 g-mol. What is the molecular formula of cacodyl ... 

J.9 You are asked to identify compound X, which was extracted from a plant seized by customs inspectors. You run a number of tests and collect the following data. Compound X is a white, crystalline solid. An aqueous solution of X turns litmus red and conducts electricity poorly, even when X is present at appreciable concentrations. When you add sodium hydroxide to the solution a reaction takes place. A solution of the products of the reaction conducts electricity well. An elemental analysis of X shows that the mass percentage composition of the compound is 26.68% C and 2.239% H, with the remainder being oxygen. A mass spectrum of X yields a molar mass of 90.0 g-moF. (a) Write the empirical formula of X. (b) Write... 

J.10 (a) White phosphorus, which has the formula P4, burns in air to form compound A, in which the mass percentage of phosphorus is 43.64%, with the remainder oxygen. The mass spectrum of A yields a molar mass of 283.9 g-mol. Write the molecular formula of compound A. (b) Compound A reacts with water to form compound B, which turns litmus red and has a mass percentage composition of 3.087% 11 and 31.60%... 

The illustrations display the percentage composition of species in the solution blue for H2P04, green for H3P04, and (below) yellow for HP042-. 

C03-0029. Determine the percentage composition of acetic acid, C2 H4 O2, the ingredient that gives vinegar its tart taste. 

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