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4 years ago

What reagent is used to test for starch

Chemistry

1 answer:

Elodia [21]4 years ago

8 0

Answer:

iodine

Explanation:

In the presence of starch, iodine turns a blue/black colour. It is possible to distinguish starch from glucose (and other carbohydrates) using this iodine solution test. For example, if iodine is added to a peeled potato then it will turn black. Benedict's reagent can be used to test for glucose.

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The product gas is then passed through a concentrated solution of KOH to remove the CO2. After passage through the KOH solution,

Kamila [148]

<u>Answer:</u> The mass percent of nitrogen gas in the compound is 13.3 %

<u>Explanation:</u>

Assuming the chemical equation of the compound forming product gases is:

$\text{Compound}\xrightarrow[CuO(s)]{Hot}N_2(g)+CO_2(g)+H_2O(g)$

Now, the product gases are treated with KOH to remove carbon dioxide.

We are given:

$p_{Total}=726torr\\P_{water}=23.8torr\\$

So, pressure of nitrogen gas will be = $p_{Total}-p_{water}=726-23.8=702.2torr$

To calculate the number of moles of nitrogen, we use the equation given by ideal gas which follows:

$PV=nRT$

where,

P = pressure of nitrogen gas = 702.2 torr = 0.924 atm (Conversion factor: 1 atm = 760 torr)

V = Volume of nitrogen gas = 31.8 mL = 0.0318 L (Conversion factor: 1 L = 1000 mL)

T = Temperature of nitrogen gas = $25^oC=[25+273]K=298K$

R = Gas constant = $0.0821\text{ L. atm }mol^{-1}K^{-1}$

n = number of moles of nitrogen gas = ?

Putting values in above equation, we get:

$0.924atm\times 0.0318L=n\times 0.0821\text{ L atm }mol^{-1}K^{-1}\times 298K\\n_{mix}=\frac{0.924\times 0.0318}{0.0821\times 298}=0.0012mol$

To calculate the mass of nitrogen gas, we use the equation:

$\text{Number of moles}=\frac{\text{Given mass}}{\text{Molar mass}}$

Molar mass of nitrogen gas = 28 g/mol

Moles of nitrogen gas = 0.0012 moles

Putting values in above equation, we get:

$0.0012mol=\frac{\text{Mass of nitrogen gas}}{28g/mol}\\\\\text{Mass of nitrogen gas}=(0.0012mol\times 28g/mol)=0.0336g$

To calculate the mass percent of nitrogen gas in compound, we use the equation:

$\text{Mass percent of nitrogen gas}=\frac{\text{Mass of nitrogen gas}}{\text{Mass of compound}}\times 100$

Mass of compound = 0.253 g

Mass of nitrogen gas = 0.0336 g

Putting values in above equation, we get:

$\text{Mass percent of nitrogen gas}=\frac{0.0336g}{0.253g}\times 100=13.3\%$

Hence, the mass percent of nitrogen gas in the compound is 13.3 %

8 0

4 years ago

Two voltaic cells are to be joined so that one will run the other as an electrolytic cell. In the first cell, one half-cell has

vladimir1956 [14]

Au/Cr cell will run as a voltaic cell and Co/Zn cell will run as an electrolytic cell.

<h3>What is an electrolytic cell?</h3>

An electrolytic cell that uses electrical energy to enable a non-spontaneous redox reaction is known as an electrolytic cell.

Certain chemicals can be electrolyzed using electrolytic cells, which are electrochemical cells.

For example, water can be electrolyzed to create gaseous oxygen and gaseous hydrogen with the use of an electrolytic cell.

The following are the three essential parts of electrolytic cells:

Cathode (which is negatively charged for electrolytic cells)

Anode (which is positively charged for electrolytic cells)

Electrolyte

The reactions for each half cell is given by

$Au^{3+}(aq) + 3e^- \rightleftharpoons Au(s)$ ; E° = 1.50 V

$Cr^{3+}(aq) + 3e^- \rightleftharpoons Cr(s)$ ; E° = –0.74 V

$Co^{2+}(aq) + 2e^- \rightleftharpoons Co(s)$ ; E° = –0.28 V

$Zn^{2+}(aq) + 2e^- \rightleftharpoons Zn(s)$ ; E° = –0.76 V

When the Au/Cr cell will run as a voltaic cell and Co/Zn cell will run as an electrolytic cell, the a difference in the voltages is produced

$E^o_{series} = E^o_{Au/Cr} - E^o_{Co/Zn}$ = 2.24 V – 0.48 V = 1.76 V

Learn more about electrolytic cell:

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7 0

1 year ago

Can someone help with this???

e-lub [12.9K]

Answer:

2Mg(s) +O₂(g) → 2MgO(s)

Explanation:

Mg(s) +O₂(g) → MgO(s)

When a chemical equation is balanced, the number of atoms of each element is equal on both sides of the arrow. We usually balance O and H last.

In this case, the number of Mg atoms is equal on both sides. Thus, let's move on to balance the O atoms. On the left side, there are 2 O atoms, while there is only 1 O atom on the left side. Thus, write a '2' in front of MgO.

Mg(s) +O₂(g) → 2MgO(s)

Now, the number of Mg atoms is not equal. Write a '2' in front of Mg to balance it.

2Mg(s) +O₂(g) → 2MgO(s)

The equation is now balanced with 2 Mg atoms and 2 O atoms on each side.

6 0

3 years ago

Sulfur is a nonmetalic mineral that has a density of 2 g/cm3. The volume of a sample of sulfur was measured to be 5.0 cm3. what

taurus [48]

Answer:

Explanation:

The mass of a substance when given the density and volume can be found by using the formula

mass = Density × volume