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3 years ago

11

What are some ideas for a compound machine for my middle school invention science project that can be useful in people's daily l

ives? I need a explanation of why it's important.

1 answer:

Zanzabum3 years ago

4 0

A toothbrush that has toothpaste in the middle so it comes preloaded. That way it is cleaner and uses more product than normal

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You have 0.14 moles of sodium chloride (NaCl). How many grams do you have? ( 1 mole of NaCl = 58 grams NaCl) *

Step2247 [10]

Answer:

Option D is correct = 8.12 grams of NaCl

Explanation:

Given data:

Moles of sodium chloride = 0.14 mol

Mass of sodium chloride = ?

Solution:

Formula:

Number of moles = mass of NaCl / Molar mass of NaCl

Molar mass of NaCl = 58 g/mol

Now we will put the values in formula.

0.14 mol = Mass of NaCl / 58 g/mol

Mass of NaCl = 0.14 mol × 58 g/mol

Mass of NaCl = 8.12 g of NaCl

Thus, 0.14 moles of NaCl contain 8.12 g of NaCl.

4 0

3 years ago

The half-life for beta decay of strontium-90 is 28.8 years. a milk sample is found to contain 10.3 ppm strontium-90. how many ye

ryzh [129]

Answer : The correct answer is 96.68 yrs

Radioactivity Decay :

it is a process in which a nucleus of unstable atom emit energy in form of radiations like alpha particle , beta particle etc .

Radioactive decay follows first order kinetics , so its rate , rate constant , amount o isotopes can be calculated using first order equations .

The first order equation for radioactive decay can be expressed as :

$ln \frac{N}{N_0} = - k*t$ ----------- equation (1)

Where : N = amount of radioisotope after time "t"

N₀ = Initial amount of radioisotope

k = decay constant and t = time

Following steps can be used to find time :

1) To find deacy constant :

Decay constant can be calculated using half life . Decay constant and half life can be related as :

$T _\frac{1}{2} = \frac{ln2}{k}$ ---------equation (2)

Given : Half life of Strontium -90 = 28.8 years

Plugging value of $T_\frac{1}{2}$ in above formula (equation 2) :

$28.8 yrs = \frac{ln 2}{ k }$

Multiply both side by k

$28.8 yrs * k = \frac{ln 2 }{k} * k$

Dividing both side by 28.8 yrs

$\frac{28.8 yrs * k}{28.8 yrs} = \frac{ln 2}{28.8 yrs}$

(ln 2 = 0.693 )

k = 0.0241 yrs⁻¹

Step 2 : To find time :

Given : N₀ = 10.3 ppm N = 1.0 ppm k = 0.0241 yrs⁻¹

Plugging these value in equation (1) as :

$ln (\frac{1.0 ppm}{10.3 ppm} ) = - 0.0241 yrs^-^1 * t$

$ln (0.0971 ) = -0.0241 yrs ^-^1 * t$

(ln 0.0971 = - 2.33 )

Dividing both side by - 0.0241 yrs⁻¹

$\frac{-2.33}{-0.0241 yrs^-^1} = \frac{-0.0241 yrs^-^1 * t}{-0.0241 yrs^-^1}$

t = 96.68 yrs

Hence the concentration of Strontium-90 will drop from 10.3 ppm to 1.0 ppm is 96.68 yrs

3 0

3 years ago

Read 2 more answers

Sanjay is learning about the elements that make up Earth’s crust. Ms. Richards, his Earth science teacher, gives him an element

oksano4ka [1.4K]

Answer:

Iron

Hope this helps! Stay safe!

(Plz vote me as brainliest)

3 0

3 years ago

How much energy would be released if 450.0 g of the substance completely reacted with oxygen?

SOVA2 [1]

Answer:

1.1853 kJ

Explanation:

4 0

3 years ago

If you have a truckload of icecream, a bucket of sauce, a box of peanuts but only 1 cherry, you can only make 1 complete sundae.

MAXImum [283]

Answer:

<em>Only 5 sundaes can be made</em>

<em>The limiting reagent is the peanuts.</em>

Explanation:

The complete question is

A perfect ice cream sundae requires exactly:

• 3 scoops of ice cream

• 2 squirts of chocolate sauce

• 1 spoon of peanuts

• 1 cherry

If you have 7 scoops of ice cream, 3 spoons of peanuts, 5 cherries and 11 squirts of sauce, you can only

make 2 complete sundaes. In this case, the icecream is the limiting reagent.

If you have a truckload of icecream, a bucket of sauce, a box of peanuts but only 1 cherry, you can only make 1 complete sundae. In this case the cherry is the limiting reagent. The limiting reagent is the term given to the ingredient (read: reactant) that has the (stoichiometrically) least amount. The other reactants are said to be in excess. In a reaction the limiting reagent will be totally consumed, and some of the reactant in excess will be leftover.

Critical thinking questions

1. If you have 20 scoops of ice cream, 14 squirts of chocolate sauce, 5 spoons of peanuts and 7 cherries,

how many sundaes can you make and which ingredient is the limiting reagent?

From the ingredients for a a complete sundae given above,

20 scoops of icecream will make 20/3 = 6.66 sundaes

14 squirts of chocolate sauce will make 14/2 = 7 sundaes

5 spoonful of peanuts will make 5/1 = 5 sundaes

7 cherries will make 7/1 = 7 sundaes

From the above, we can work out that only 5 sundaes can be made, and the limiting agent here is peanuts, which has the least amount of sundae that can be made from its available amount.

5 0

3 years ago