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2 years ago

how many moles of silicon are in 245 g of silicon? a. 8.72 mol b. 28.0 mol c. 1.10 10-1 mol d. 6.90 103 mol

1 answer:

7 0

Atomic mass silicon = 28.085 u

1 mol Si ---------------- 28.085 g
? ------------------------ 245 g

245 x 1 / 28.085 =><span> 8.72 mol</span>

<span>answer A</span>

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How do forensic scientists determine the time of death? There are timely pieces of evidence that help scientists with this task.

UNO [17]

I have done some research as well as asking some friends. This is what I came up with. Not sure if it is 100% correct.

step = time after death

1. Livor Mortis = 20-30 minutes

2. Eyes film (cloud) = 2 hours

3. Rigor Mortis begins = 4-6 hours

4. Empty small intestines = 12 hours

5. Bloating = 3-5 days

6. Decay

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3 years ago

Calculate the number of atoms in 35 g of carbon. Calculate the number of atoms in 75 g of bromine.

nata0808 [166]

Answer:

Explanation:

To calculate the number of atoms in a formula, the weight of a sample, its atomic mass from the periodic table and a constant known as Avogadro’s number are needed.

Step 1: Find the Molar Mass of the Formula

Find a periodic table of elements to find the molar mass of your sample. If your sample is made of one element, like copper, locate the atomic mass on the periodic table. Atomic mass is usually listed below the symbol for that element.

The atomic mass of carbon and bromine is 63.55 atomic mass units. This formula mass is numerically equal to the molar mass in grams/mole, and this means copper is 63.55 grams/mole.

Whether you use an individual element like copper or a molecule, the procedure for finding the atoms in a formula remains the same.

Find the molar mass of carbon and bromine on the periodic table: 63.55 grams/mole.

Understanding the Mole: The mole (often abbreviated as mol) listed above is a unit of measurement. If you sold eggs, you would talk about them in the dozens, not one by one.

A mole is a certain amount, too. If chemists want to speak about incredibly small atoms and molecules, an amount far greater than a dozen is needed. A mole is Avogadro’s number of items: 6.022 × 1023.

1 mole of C atoms = 6.022 × 1023 C atoms

1 mole of Br atoms = 6.022 × 1023 S atoms

1 mole of CBrmolecules = 6.022 × 1023 CBr molecules

1 mole of pennies = 6.022 × 1023 pennies

To give an idea of how large this number is, 1 mole of pennies would be enough money to pay all the expenses of each country on earth for about the next billion years.

Step 2: Find the Number of Moles

The example is 35 grams of C and . Change that into moles using the molar mass you found in Step 1. Chemists use ratios for this calculation.

Start with what you know and add in the molar mass ratio, so the units will cancel:

35g of C× 1 mol C/ 12 g C = 2.92mol of C

Step 3: Convert Moles to Atoms Using Avogadro’s Number

Once the amount of moles is known, the number of atoms in the formula may be calculated using Avogadro’s number. Again, use the ratio format.

Notice the number of moles is used from Step 2 to start the calculation from moles to atoms:

2.92 mol of C× 6.022 x 1023 atoms / 1 mol of C = 3.13 x 1023 molecules

To answer your example question, there are 3.13 × 1023 atoms in 32.80 grams of carbon.

Steps 2 and 3 can be combined. Set it up like the following:

32.80 g of C × 1 mol Cu / 159.17 g C × 6.022 x 1023 atoms / 1 mol of C = 3.13 x 1023 atoms in 32.80 grams of carbon

Several online sites have a number of atoms calculator. One is the Omni Calculator and is listed in the Resources section, but you’ll still need to know how to calculate molar mass (Step 1).

Historical Note: Why Is It Called Avogadro's Number?

Avogadro’s number is named after Amedeo Avogadro (1776-1856), an Italian scientist that hypothesized that equal volumes of gases at the same temperature and pressure will have the same number of particles.

Avogadro did not propose the constant, 6.022 ×1023, but because of his contributions to science, the constant was named after him. Incidentally, Avogadro first introduced his gas theory in 1811, and it was ignored for 50 years.

5 0

2 years ago

Malonic acid, h2c3h2o4, is a diprotic acid with ka1= 1.5 x 10-3and ka2= 2.0 x 10-6. what is the concentration of the malonate an

Bess [88]

In a 0.15 m solution of malonic acid, the amount of the malonate anion, c3h2o42-, is $1.68*10^{-4} M$ .

Explanation:

For the first equlibria;

initial concentration of $H_{2}C_{3}H_{2}OH=0.15$

initial concentration of $HC_{3}H_{2}O_{4}^{-} =0$

initial concentration of $H^{+} =0$

Let concentration change of $H_{2}C_{3}H_{2}OH=-x$

Let concentration change of $HC_{3}H_{2}O_{4}^{-} =+x$

Let concentration change of $H^{+} =+x$

Let concentration in equilibrium state of $H_{2}C_{3}H_{2}OH=0.15-x$

Let concentration in equilibrium state of $HC_{3}H_{2}O_{4}^{-} =x$

Let concentration in equilibrium state of $H^{+} =x$

Therefore, $Ka_{1}=\frac{x*x}{0.15-x}=\frac{1.5*10^{-3}}{1} =\frac{x^{2}}{0.15-x}$

$x^{2}+0.0015x-0.000225=0$

Which is a quadratic equation in x, solving it gives;

$x=0.01427$

Therefore, $HC_{3}H_{2}O_{4}^{-} =x= 0.01427M$

Now for the second equlibria;

initial concentration of $HC_{3}H_{2}O_{4}^{-}=0.01427$

initial concentration of $C_{3}H_{2}O_{4}^{2-} =0$

initial concentration of $H^{+} =0$

Let concentration change of $HC_{3}H_{2}O_{4}^{-}=-x$

Let concentration change of $C_{3}H_{2}O_{4}^{2-} =+x$

Let concentration change of $H^{+} =+x$

Let concentration in equilibrium state of $HC_{3}H_{2}O_{4}^{-}=0.01427-x$

Let concentration in equilibrium state of $C_{3}H_{2}O_{4}^{2-} =x$

Let concentration in equilibrium state of $H^{+} =x$

Therefore, $Ka_{2}=\frac{x*x}{0.01427-x}=\frac{2.0*10^{-6}}{1} =\frac{x^{2}}{0.01427-x}$

$2.854*10^{-8}-(2.0*10^{-6})x=x^{2}$

Therefore, $C_{3}H_{2}O_{4}^{2-} =x= 1.68*10^{-4}M$

<h3>What is a malonic acid?</h3>

The chemical formula of malonic acid is CH2(COOH)2. Malonates include the ionized form of malonic acid as well as its esters and salts. For instance, the diethyl ester of malonic acid is called diethyl malonate.

Polyester and polymers both employ malonic acid as a precursor. Both the scent business and the flavoring sector utilize it. It is employed to regulate acidity. Malonic acid contributes to the production of fatty acids in people. Malonic acid has been found in a number of foods outside of the human body, including red beets, corn, scarlet beans, common beets, and cow milks, although its presence has not been defined. The group of organic substances known as dicarboxylic acids and derivatives includes malonic acid, also known as malonate or H2MALO.

To know more about malonic acid, visit:

brainly.com/question/13943912?referrer=searchResults

#SPJ4

4 0

1 year ago

The speed of light in a vacuum is 2.998 × 10 8 8 m/s. How long does it take for light to circumnavigate the Earth, which has a c

svp [43]

Answer:- 0.134 seconds

Solution:- The speed is given as $2.988*10^8\frac{m}{s}$ and the circumference is 24900 miles which is same as the distance light have to covered. It asks to calculate the time required to cover this distance by the light.

We need to do unit conversion from miles to meter as the speed is given in meter per second.

1 mile = 1609.34 meter

So, $24900mile(\frac{1609.34meter}{mile})$

= 40072566 meters

Know that, $speed=\frac{distance}{time}$

It's rearranged to time as, $time=\frac{distance}{speed}$

Let's plug in the values in it:

$time=\frac{40072566meter}{2.988*10^8\frac{meter}{second}}$

= 0.134 seconds

So, the light would take 0.134 seconds to travel the mentioned speed. The answer without the unit is 0.134.

8 0

2 years ago

Difference between rapid combustion and spontaneous combustion.

statuscvo [17]

Answer: The difference between rapid combustion and spontaneous combustion...

Explanation:

Rapid combustion is a form of combustion, otherwise known as a fire, in which large amounts of heat and light energy are released, which often results in a flame.Whereas spontaneous combustion is the ignition of organic matter (e.g. hay or coal) without apparent cause, typically through heat generated internally by rapid oxidation.

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2 years ago