Determination course

Determination of active acidity of fruit-berry juice with the help of pH-metre

Devices, laboratory ware, reactants: pH-metre, chemical glasses vol. 50 ml, a glass funnel, measure flasks vol. of 250 cm³, fixanals for preparation of the buffer solutions, the distilled water, a filtering paper, absorbent cotton.

Determination course For determination pH use pH-metres or universal ionometers with a measuring glass electrode and chlorsilver comparison electrode.

Before carrying out of measurements electrodes carefully wash out the distilled water and adjust the device by the buffer solutions prepared from fixanals. It is recommended to checking accuracy of the device use a buffer solution with pH, near to pH of an investigated solution.

For carrying out of measurements of active acidity from the prepared test in a bottle vol. 50 ml take such quantity of a product which provide immersing of electrodes. Readout pH level count by the scale when the device scale will stop. Readout of results takes to within 0,1 (point one).

Measurement of pH repeat by three times, each time taking out electrodes from a solution and during measurement again immersing them in a solution.

Determination of active acidity of fruit juice with the help of a test paper

The method is based on colouring of a test paper during its wetting by an investigated solution and comparable the obtained colouring with a comparison scale.

The method is applied for the rough estimate of pH level.

For measurement take a strip of a universal test paper and by means of a glass stick put a drop of an investigated solution on a strip. Using a colour scale of comparison enclosed to test paper, by the obtained colour of the indicator find value of pH level, that answers the given colour.

Determination of titrated acidities in vegetable canned food and fruit juice using a metric burette

Devices, laboratory ware, reactants: pipettes vol. of 20 and 50 ml, conic bulbs vol. of 250 cm³, measuring flasks vol. 250 cm³, a funnel, burette for titration, technical balance, a chemical glass, 1 %-s' solution of phenolphtalein, 0,1 g of a KOH solution (potassium caustic), the distilled water, a filtering paper.

Determination course

For research weigh 25 g of crushed product on technical scales to within 0,01 Навеску transfer the hot distilled water through a funnel from chemical glasses to a measured flask vol. of 250 ml and add the distilled water to half of flask. Leave on since minute, periodically mixing. Then cool a flask to a room temperature and add the distilled water to a label, mix a flask further. Also filter through the filter or cotton to conic flask vol. of 250 ml. Take 50 ml of the obtained filtrate with a pipette and add 3-5 drops of 1 %-ethanol solution of phenolphtalein and titrate with 0,1 g a solution of caustic sodium till the pink coloring occurrence.

In case of determination of titrated acidities in liquid products (juice, a brine, etc.) Take 25 ml of a liquid in a measured flask vol. of 250 ml and add the distilled water to a label. Carefully mix contents of a test tube and take 50 cm³ in a conic flask for titration.

Calculation of a mass fraction, % titrated acidities X_tc calculation carryed out by such formula:

,

Where V₁ – quantity of the 0,1M solution of alkali used for titration, cm³; K - recalculation factor on acid: apple - 0,0067; lemon - 0,0064; acetic - 0,0060; dairy - 0,0090; wine - 0,0075; V₀ - volume to which it is finished charge, ml; V₂ - volume of the solution taken for titration, ml; m -charge (volume for liquid products) an investigated product, g (cm³).

Аналіз одержаних результатів

Студент відповідно до завдань повинен дати порівняльну характеристику методам визначення кислотності у сировині та готової продукції.

Запитання для самоперевірки

1. Дайте визначення реакції середовища

2. Дайте визначення загальної або титрованої і активної кислотності та лужності.

3. Які існують індикатори? Як їх використовують під час визначення лужності і кислотності продуктів?

4. Як працює рН-метр?

5. Які методи визначення рН ви знаєте?

Laboratory work 2

Starch, yeast and flour acidity determination. Titrated acidity.

Дата добавления: 2015-11-14