Chemistry 41 - Balancing chemical equations
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Chemistry 40
H3C6H5O7 is the molecular formula for citric acid.

Malic acid is an organic compound with the formula HO2CCH2CHOHCO2H. This dicarboxylic acid is the active ingredient in many sour or tart foods. Malic acid is found mostly in unripe fruits.

The salts and esters of malic acid are known as malates. The malate anion is an intermediate in the citric acid cycle.


Chemistry 39
What is the difference between compound and mixture?

A compound is a material, in which atoms of different elements are chemically held to one another. A mixture is a substance made by combining two or more different materials in such a way that no chemical reaction occurs.

A mixture can usually be separated back into its original components, a compound can not.


Chemistry 38 - pH Indicator
A pH indicator is a halochromic chemical compound that is added in small amounts to a solution so that the pH (acidity or basicity) of the solution can be determined visually. Hence a pH indicator is a chemical detector for hydronium ions (H3O+ or hydrogen ions (H+) in the Arrhenius model). Normally, the indicator causes the color of the solution to change depending on the pH. At 25° Celsius, considered the standard temperature, the pH value of a neutral solution is 7.0.
Solutions with a pH value below 7.0 are considered acidic, whereas solutions with pH value above 7.0 are basic. As most naturally occurring organic compounds are weak protolytes, carboxylic acids and amines, pH indicators find many applications in biology and analytical chemistry. Moreover, pH indicators form one of the three main types of indicator compounds used in chemical analysis. For the quantitative analysis of metal cations, the use ofcomplexometric indicators is preferred, whereas the third compound class, the redox indicators, are used in titrations involving a redox reaction as the basis of the analysis.

Application

pH indicators are frequently employed in titrations in analytic chemistry and biology experiments to determine the extent of a chemical reaction. Because of the subjective determination of color, pH indicators are susceptible to imprecise readings. For applications requiring precise measurement of pH, a pH meter is frequently used.

Tabulated below are several common laboratory pH indicators. Indicators usually exhibit intermediate colors at pH values inside the listed transition range. For example, phenol red exhibits an orange color between pH 6.8 and pH 8.4. The transition range may shift slightly depending on the concentration of the indicator in the solution and on the temperature at which it is used.

IndicatorLow pH colorTransition pH rangeHigh pH color
Gentian violet (Methyl violet 10B)yellow0.0–2.0blue-violet
Leucomalachite green (first transition)yellow0.0–2.0green
Leucomalachite green (second transition)green11.6–14colorless
Thymol blue (first transition)red1.2–2.8yellow
Thymol blue (second transition)yellow8.0–9.6blue
Methyl yellowred2.9–4.0yellow
Bromophenol blueyellow3.0–4.6purple
Congo redblue-violet3.0–5.0red
Methyl orangered3.1–4.4orange
Bromocresol greenyellow3.8–5.4blue
Methyl redred4.4–6.2yellow
Methyl redred4.5–5.2green
Azolitminred4.5–8.3blue
Bromocresol purpleyellow5.2–6.8purple
Bromothymol blueyellow6.0–7.6blue
Phenol redyellow6.8–8.4red
Neutral redred6.8–8.0yellow
Naphtholphthaleincolorless to reddish7.3–8.7greenish to blue
Cresol Redyellow7.2–8.8reddish-purple
Phenolphthaleincolorless8.3–10.0fuchsia
Thymolphthaleincolorless9.3–10.5blue
Alizarine Yellow Ryellow10.2–12.0red
Litmusred4.5-8.3blue



abstracted from: http://en.wikipedia.org/wiki/PH_indicator

Chemistry 37 - Find you pH level!

Chemistry 36 - Lime water

Lime water is the common name for saturated calcium hydroxide solution. It is sparsely soluble. Its chemical formula is Ca(OH)2. Since calcium hydroxide is only sparsely soluble, i.e. ca. 1.5g per liter at 25°C[1], there is no visible distinction to clear water. Attentive observers would notice a slightly earthy smell. It is clearly distinguishable by the alkaline taste of the calcium hydroxide. The term is based on the mineral sense of lime, rather than the fruit sense of lime. When exposed with carbon dioxide, lime water turns into a milky solution.

While lime water is a clear solution, milk of lime on the other hand is a suspension of calcium hydroxide particles in water. These particles give it the milky aspect. It is commonly produced by reacting quicklime (calcium oxide) with an excess of water - usually 4 to 8 times the amount of water to the amount of quicklime. Reacting water with quicklime is sometimes referred to as "slaking" the lime. The calcium oxide will convert to the hydroxide according to the following reaction scheme:

CaO + H2O → Ca(OH)2

This reaction is strongly exothermic and will generate enough heat to bring the suspension to a scalding temperature. At a ratio of 2 parts water to 1 part lime (by weight), the generated heat is sufficient to bring the suspension, i.e. the water in it, to boil. Milk of lime is an alkaline with a pH of 12.3. It is commonly used in the chemical industry and as a neutralizing agent in municipal waste water treatment. While it has a multitude of other uses, it is best known in its (historical) use as a paint: lime wash or whitewash.





abstracted from: http://en.wikipedia.org/wiki/Lime_water


Chemistry 35 - Calcium Carbonate
Calcium carbonate is a chemical compound with the chemical formula CaCO3. It is a common substance found in rock in all parts of the world, and is the main component of shells of marine organisms, snails, pearls, and eggshells. Calcium carbonate is the active ingredient in agricultural lime, and is usually the principal cause of hard water. It is commonly used medicinally as a calcium supplement or as an antacid, but excessive consumption can be hazardous.