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3 years ago

How does a scientist use observations to help create the

Chemistry

1 answer:

alexira [117]3 years ago

8 0

Answer:

They use hypotheses to guess a result based on what they already know. Observations are used to record the results of an experiment. Predictions are used to have an expected outcome of a test, thinking the hypothesis is correct. Experiments are used to test the hypothesis.

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5 points

Orlov [11]

Answer:

The correct option is (a).

Explanation:

We need to find the product of given numbers.

First number = 29.5

Second number = 240

Product of two numbers = 29.5 × 240

= $\dfrac{295}{10}\times 240$

Zeroes from numerator and denominator get cancelled.

So,

$=295\times 24\\\\=7080$

Hence, the correct option is (a).

7 0

3 years ago

Which of the following possess the greatest concentration of hydroxide ions?

jek_recluse [69]

Answer : The correct option is (d) a solution of 0.10 M NaOH

Explanation :

(a) a solution of pH 3.0

First we have to calculate the pOH.

$pH+pOH=14\\\\pOH=14-pH\\\\pOH=14-3.0=11$

Now we have to calculate the $OH^-$ concentration.

$pOH=-\log [OH^-]$

$11=-\log [OH^-]$

$[OH^-]=1.0\times 10^{-11}M$

Thus, the $OH^-$ concentration is, $1.0\times 10^{-11}M$

(b) a solution of 0.10 M $NH_3$

As we know that 1 mole of $NH_3$ is a weak base. So, in a solution it will not dissociates completely.

So, the $OH^-$ concentration will be less than 0.10 M

(c) a solution with a pOH of 12.

We have to calculate the $OH^-$ concentration.

$pOH=-\log [OH^-]$

$12=-\log [OH^-]$

$[OH^-]=1.0\times 10^{-12}M$

Thus, the $OH^-$ concentration is, $1.0\times 10^{-12}M$

(d) a solution of 0.10 M NaOH

As we know that $NaOH$ is a strong base. So, it dissociates to give $Na^+$ ion and $OH^-$ ion.

So, 0.10 M of $NaOH$ in a solution dissociates to give 0.10 M of $Na^+$ ion and 0.10 M of $OH^-$ ion.

Thus, the $OH^-$ concentration is, 0.10 M

(e) a $1\times 10^{-4}M$ solution of $HNO_2$

As we know that 1 mole of $HNO_2$ in a solution dissociates to give 1 mole of $H^+$ ion and 1 mole of $NO_2^-$ ion.

So, $1\times 10^{-4}M$ of $HNO_2$ in a solution dissociates to give $1\times 10^{-4}M$ of $H^+$ ion and $1\times 10^{-4}M$ of $NO_2^-$ ion.

The concentration of $H^+$ ion is $1\times 10^{-4}M$

First we have to calculate the pH.

$pH=-\log [H^+]$

$pH=-\log (1.0\times 10^{-4})$

$pH=4$

Now we have to calculate the pOH.

$pH+pOH=14\\\\pOH=14-pH\\\\pOH=14-4=10$

Now we have to calculate the $OH^-$ concentration.

$pOH=-\log [OH^-]$

$10=-\log [OH^-]$

$[OH^-]=1.0\times 10^{-10}M$

Thus, the $OH^-$ concentration is, $1.0\times 10^{-10}M$

From this we conclude that, a solution of 0.10 M NaOH possess the greatest concentration of hydroxide ions.

Hence, the correct option is (d)

3 0

3 years ago

Magma that is rich in feldspar and silica is called?

weeeeeb [17]

Answer:

<h3>magma that is rich in feldspar and silica is called STRATOVOLCANO.</h3>

3 0

3 years ago

How can you tell if glucose is present?

rosijanka [135]

Answer:

Plants use photosynthesis to make glucose. Glucose is also know as sugar. You can tell it is present if the plant receives sunlight as well as water.

Explanation:

MARK BRAINLIEST

4 0

3 years ago

Calculate the mass of Na2O that can be produced by the chemical reaction of 4.0 grams of sodium with excess oxygen in the reacti

e-lub [12.9K]

Answer:

The mass of Na₂O that can be produced by the chemical reaction of 4.0 grams of sodium with excess oxygen in the reaction is 5.39 grams.

Explanation:

You know the balanced reaction:

4 NA + O₂ ⟶ 2 Na₂O

By stoichiometry of the reaction (that is, the relationship between the amount of reagents and products in a chemical reaction) react and are produced:

Na: 4 moles
O₂: 1 mole
Na₂O: 2 moles

Being:

Na: 23 g/ole
O: 16 g/mole

the molar mass of the compounds participating in the reaction is:

Na: 23 g/mole
O₂: 2*16 g/mole= 32 g/mole
Na₂O: 2*23 g/mole +16 g/mole= 62 g/mole

Then by stoichiometry of the reaction they react and are produced:

Na: 4 moles* 23 g/mole= 92 g
O₂: 1 mole*32 g/mole= 32 g
Na₂O: 2 moles* 62 g/mole= 124 g

Then you can apply the following rule of three: if 92 grams of Na produce 124 grams of Na₂O, 4 grams of Na, how much mass of Na₂O does it produce?

$massofNa_{2}O =\frac{4 grams of Na*124 gramsofNa_{2}O }{92 grams of Na}$

mass of Na₂O=5.39 g

The mass of Na₂O that can be produced by the chemical reaction of 4.0 grams of sodium with excess oxygen in the reaction is 5.39 grams.

8 0

3 years ago