Concentration Definition (Chemistry)

Concentration Definition (Chemistry) In chemistry, the word concentration relates to the components of a mixture or solution. Here is the definition of concentration and a look at different methods used to calculate it. Concentration Definition In chemistry, concentration refers to the amount of a substance per defined space. Another definition is that concentration is the ratio of solute in a solution to either solvent or total solution. Concentration usually is expressed in terms of mass per unit volume. However, the solute concentration may also be expressed in moles or units of volume. Instead of volume, concentration may be per unit mass. While usually applied to chemical solutions, concentration may be calculated for any mixture. Two related terms are concentrated and dilute. Concentrated refers to chemical solutions that have high concentrations of a large amount of solute in the solution. Dilute solutions contains a small amount of solvent compared with the amount of solvent. If a solution is concentrated to the point where no more solute will dissolve in the solvent, it is said to be saturated. Unit Examples of Concentration: g/cm3, kg/l, M, m, N, kg/L How to Calculate Concentration Concentration is determined mathematically by taking the mass, moles, or volume of solute and dividing it by the mass, moles, or volume of the solution (or less commonly, the solvent). Some examples of concentration units and formulas include: Molarity (M) - moles of solute / liters of solution (not solvent!)Mass Concentration (kg/m3 or g/L) - mass of solute / volume of solutionNormality (N) - grams active solute / liters of solutionMolality (m) - moles of solute / mass of solvent (not mass of solution!)Mass Percent (%) - mass solute / mass solution x 100% (mass units are the same unit for both solute and solution)Volume Concentration (no unit) - volume of solute / volume of mixture (same units of volume for each)Number Concentration (1/m3) - number of entities (atoms, molecules, etc.) of a component divided by the total volume of the mixtureVolume Percent (v/v%) - volume solute / volume solution x 100% (solute and solution volumes are in the same units)Mole Fraction (mol/mol) - moles of solute / total moles of species in the mixtureMole Ratio (mol/mol) - moles of solute / total moles of all other species in the mixtureMass Fraction (kg/kg or parts per) - mass of one fraction (could be multiple solutes) / total mass of the mixture Mass Ratio (kg/kg or parts per) - mass of solute / mass of all other constituents in the mixturePPM (parts per million) - a 100 ppm solution is 0.01%. The parts per notation, while still in use, has largely been replaced by mole fraction.PPB (parts per billion) - typically used to express contamination of dilute solutions Some units may be converted from one to another, however, its not always a good idea to convert between units based on the volume of solution to those based on mass of solution (or vice versa) because volume is affected by temperature. Strict Definition of Concentration In the strictest sense, not all means of expressing the composition of a solution or mixture are termed concentration. Some sources only consider mass concentration, molar concentration, number concentration, and volume concentration to be true units of concentration. Concentration Versus Dilution Another common usage of the term concentration refers to how concentrated a solution is. A concentrated solution contains as much solute as it can hold. Chemists often prefer to call such a solution saturated. In contrast, a solution that contains few solute particles is said to be dilute. In order to concentrate a solution, either more solute particles must be added or some solvent must be removed. If the solvent is nonvolatile, a solution may be concentrated by evaporating or boiling off solvent. Dilutions are made by adding solvent to a more concentrated solution. Its common practice to prepare a relatively concentrated solution, called a stock solution, and use it to prepare more dilute solutions. This practice results in better precision than simply mixing up a dilute solution because it can be difficult to obtain an accurate measurement of a tiny amount of solute. Serial dilutions are used to prepare extremely dilute solutions. To prepare a dilution, stock solution is added to a volumetric flask and then diluted with solvent to the mark. Source IUPAC, Compendium of Chemical Terminology, 2nd ed. (the Gold Book) (1997).

Peer review Coursework Example | Topics and Well Written Essays - 500 words

Peer review - Coursework Example why the University of Marion introduced the LessThanUThink campaign in order to sensitize students on the importance to focus on their studies rather than engage in irresponsible activities such as excessive alcohol consumption. The author should include the effects of alcohol on student performance and graduation rate. It is significant to note that as discussed in the proposal, the author gathered evidence from University students that they usually consume very large volumes of alcohol mostly during the weekends to get wasted. According to them, they do this for fun and an individual can end up guzzling up to over ten drinks in a night. However, this heavy drinking results in personal tragedy for college students and their families. Yes, the draft proposal persuades in the way the author has answered the problem of the proposal. The author has stated the reasons why the campaign was launched. The campaign in the University was successful since after the campaign was launched, it has assisted educate students when others engage in irresponsible drinking. There is no need for change or reorganization of the paper but the author should state the research design of the study and the methods they used to gather information about binge drinking in the University of Marion. The author was very keen and specific thus they avoided any form of repetitiveness. The most interesting part is the statistics about the past drinking behavior of students at the University of Marion. The statistics were shocking and needed immediate intervention to avoid further damage to the students and the reputation of the University. For example, I learned that about 25 percent of college students report academic consequences of their drinking including missing class, falling behind, doing poorly on exams or papers, and receiving lower grades

Econometrics Essay Example | Topics and Well Written Essays - 750 words - 2

Econometrics - Essay Example d) Assume that you run a regression with 223 observations. The dependent variable is ‘annual salary’ and there are 3 independent variables ‘work experience in years’, ‘education duration in years’ and ‘number of employees in company’. The regression yields following result for the variable ‘number of employees in company’: e) A researcher wants to find out whether age has an effect on how happy people are. The researcher runs a regression with the dependent variable ‘happiness score’ (0 to 10 with 10 being extremely satisfied) and the independent variable ‘age’ (in years). The modelling results show that age is not significant. You also have a look at the residual plot (shown below). Please explain why the residual plot indicates that the regression generated by the researcher is misleading. Discuss what relationship you expect between age and happiness. Outline how you could work this into the initial regression model and hence, improve it (10 marks). From the analysis of the residual below it can be observed that the residua are symmetrical. The residual also have constant variance. This means that the assumption of constant variance is fulfilled. We therefore expect a significant relationship between the age and happiness. To improve the initial regression model, we would ensure that other variables that influence the happiness are introduced into the regression model. f) You want to know whether people with higher incomes are happier. Your friend has run a survey in their company and run a regression on the data. The dependent variable is ‘happiness score’ (0 to 10 with 10 being extremely satisfied). There is only one independent variable: ‘monthly income’ (in  £). Your friend sends you the gretl output of the regression via email. Unfortunately, the file got corrupted and only the critical F-value is legible (see below). Using this output, show that ‘monthly income’ is indeed highly significant (provide