In this reaction, the chromium is reduced, from cr6+ to cr3+, causing a color change in the solution, signaling the endpoint. determine the mass percent ethanol in a 40.0 g blood sample, if the sample required 22.6 ml of 0.05 m k2cr2o7 to react completely with all the ethanol answers

Using the information provided in the question, the percentage by mass of ethanol in the blood is 0.1949%.

Explanation:

The balanced equation for the reaction can be written as:

3CH3CH2OH + 2K2Cr2O7+ 16H+ >>>> 3CH3COOH + 4Cr3+ + 4K+ + 11H2O. This will be used to solve the problem.

The no of moles of K2Cr2O7 used = concentration X volume in dm cube.

= 0.05 X 22.6/1000 = 1.13/1000 = 0.00113 moles of K2Cr2O7 was used.

From the balanced equation above, 3 moles of ethanol will react with 2 moles of K2Cr2O7.

Therefore, 0.00113 X 3/2 moles of ethanol would have been in the blood of the subject = 0.001695 moles of ethanol.

Remember that no of moles = mass/molar mass. Then mass = moles X molar mass.

The molar mass of ethanol is 46g/mole.

Then mass = 0.001695 X 46 = 0.07797gram of Ethanol was in the blood.

Percentage by mass in blood is: 0.07797/40 X 100 = 0.1949%

- lead + phosphoric acid = hydrogen + lead(ii) phosphate

a mercury barometer is a device that uses the physical properties of mercury in a tube to measure barometric pressure. mercury barometers are used for : -

1. measurement of atmospheric pressure  

2. determining the altitude of a place

3. weather forecasting

4. calibration and checking of aneroid barometers

5. application in fluid mechanics

6. measurement of pressure in aircrafts

7. surface weather analysis

8. preparation of barographs

9. usage in physical sciences like physics, astronomy & chemistry

10. preparation of aircraft altimeters

characteristics of mercury barometer : -

1.used to define and measure atmospheric pressure.

2.on the average at sea level the column of mercury rises to a height of about 760 mm.

3.this quantity is equal to 1 atmosphere.

4.it is also known as standard atmospheric pressure.

5.a barometer in which the weight of a column of mercury in a glass tube with a sealed top is balanced against that of the atmosphere pressing on an exposed cistern of mercury at the base of the mercury column, the height of the column varying with atmospheric pressure.