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3 years ago

Anthracite is so hard and pure it is also referred to as a _____.

1 answer:

6 0

Anthracite is also referred to as hard coal because it is so hard and pure. It is very hard and highly compacted with variety of coal that has submetallic luster. It has highest carbon content, the lowest impurities, and highest density of energy of all the coal deposits.

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Protein x has an absorptivity of 0.4 ml·mg-1 ·cm-1 at 280 nm. What is the absorbance at 280 nm of a 2.0 mg ·ml-1 solution of pro

Evgen [1.6K]

Absorbance measures the ability of the substance to absorb light at a specific wavelength.

Absorbance is also equal to the product of molar absorptivity, path length and molar concentration.

The mathematical expression is given as:

$A= \epsilon l c$ (1)

where, A = absorbance

$\epsilon$ = molar absorptivity

l = path length

c = molar concentration.

The above formula is said to Beer's Law.

Absorptivity of protein x = $0.4 mLmg^{-1}cm^{-1}$

Path length = 1 cm

Molar concentration = $2.0 mg mL^{-1}$

Put the values in formula (1)

$Absorbance at 280 nm = 0.4 mL mg^{-1}cm^{-1}\times 1 cm \times 2.0 mg mL^{-1}$

= $0.8$

Thus, absorbance at 280 nm = $0.8$

3 0

4 years ago

SOMEBODY PLEASE HELPP I HAVE LIKE 10 TEST THAT I HAVE TO TAKE AND I WAS OUT SICK THOSE DAYS

snow_lady [41]

Answer: the 1st one is B, 2 is A, 3 is A, 4 is a or D for this one, 5 is c, 6 is b, 7 is b, 8 is d, 9 is a, 10 is b those are my best guess and if that did work I'm sorry I didn't help you and take care also have a great day.

4 0

3 years ago

Why is it easier for water molecules to bond together than it is for other molecules to bond together?

laiz [17]

Answer:

We know that there are two types of forces ,one is cohesive force between same molecule and other one is adhesive force between two different type of molecule.

In the water cohesive is more dominate than the adhesive force that is why it is for water molecule bond together.Another reason is that the hydrogen molecule have low electro negativity than the oxygen molecule that is oxygen molecule try to pull hydrogen and form the hydrogen bond.

6 0

3 years ago

Consider the following intermediate chemical equations.

Zinaida [17]

Answer:

The first choice, $-205.7\; \rm kJ$ .

Explanation:

Let the three reactions, where the enthalpy change were known, be called (1), (2), and (3).

The goal is to find the enthalpy change of the fourth equation. Assume that this equation can be written as $x \times (1) + y \times (2) + z \times (3)$ for some $x$ , $y$ , and $z$ (might not be whole numbers or take positive values.) Then, by Hess's Law, the enthalpy change of that reaction would be $x \cdot \Delta H_1 + y \cdot \Delta H_2 + z \cdot \Delta H_3$ .

To find these $x$ , $y$ , and $z$ , consider: what combination of reaction (1), (2), and (3) would give the fourth reaction?

Imagine that the coefficients are positive for all the reactants, and negative for all the products.

For example: in (1), $\rm H_2\; (g)$ has a coefficient of $2$ . However, since it is on the the product side of (1), its value should be $-2$ . Also, in (3)

Since there is no $\rm H_2\; (g)$ in the desired equation, the value of $x$ , $y$ , and $z$ should ensure that $-2x + z = 0$ .

Another example: $\rm CH_4\; (g)$ is on the reactant side of the first reaction. Its coefficient in the equation is $1$ , so that corresponds to $+1$ . Since $\rm CH_4$ is neither in (2) nor in (3), the value of

In the desired equation, $\rm CH_4\; (g)$ is on the reactant side with a coefficient of $1$ . As a result, the value of $x$ , $y$ , and $z$ should ensure that $x = 1$ .

One such equation can be found for each species in the reactions.

$\displaystyle \begin{cases}x = 1 & \left(\text{For $\mathrm{CH_4\; (g)}$}\right) \\ -x - y= 0 & \left(\text{For $\mathrm{C\; (s)}$}\right) \\ -2\, x + z = 0 & \left(\text{For $\mathrm{H_2\; (g)}$}\right) \\ y = -1 & \left(\text{For $\mathrm{CCl_4\; (g)}$}\right) \\ -2\, y + z= 4 & \left(\text{For $\mathrm{Cl_2\; (g)}$}\right) \\ -2\, z = -4 & \left(\text{For $\mathrm{HCl\; (g)}$}\right)\end{cases}$ .

Solve this system of equations for $x$ , $y$ , and $z$ (this approach works only if at least one solution exists.) In this case,

$\displaystyle \begin{cases}x = 1 \\ y = -1 \\ z = 2\end{cases}$ .

Calculate the enthalpy change of the desired reaction:

$\begin{aligned}\Delta H &= x\times \Delta H_1 + y \times \Delta H_2 + z \times \Delta H_3 \\ &= 1 \times 74.6 + (-1) \times 95.7 + 2 \times (-92.3) \\ &= -205.7\; \rm kJ\end{aligned}$ .

4 0

3 years ago

Find the amount of red food coloring (in grams) necessary to add to 50 grams of water to prepare a 15% solution of red food colo

olga nikolaevna [1]

Answer:

9 grams

Explanation:

Percentage is a concentration unit that describes the amount of a solute in 100 parts of total substance (solution).

The weight percent of a solution is given by the formula:

% (w/w) = (mass of solute / mass of solution) × 100

Here, the red food coloring is the solute, water is the solvent, and the solution is the mixture.

You know the mass of water (50 g) and the percentage (15%), thus you can calculate the mass of red food coloring (x) in this way:

1. Mass of solution

Mass of solution = mass of red food coloring + mass of water

mass of solution = x + 50

2. Percent

$%=x/(x+50)\times 100=15$ % = x / (x + 50) × 100 = 15

3. Solve for x:

x / (x + 50) = 0.15

x = 0.15(x + 50)

x = 0.15x + 7.5

0.85x = 7.5

x = 8.82 g

Round to two one significant figure, because the number 50 grams has one significant figure.

x = 9 grams.

8 0

4 years ago