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3 years ago

Humans first appeared in the _____ period.

Chemistry

2 answers:

Ira Lisetskai [31]3 years ago

6 0

Answer:

They first appeared in the fossil record around 66 million years ago, soon after the Cretaceous–Paleogene extinction event that eliminated about three-quarters of plant and animal species on Earth, including most dinosaurs.

Explanation:

vlabodo [156]3 years ago

4 0

Answer:

A or b I learned this in history

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Jupiter revolves around the sun in a predictable pattern because

Misha Larkins [42]

Jupiter revolves around the Sun in a predictable pattern because the force of gravity between Jupiter and the Sun maintains the orbit.

8 0

2 years ago

A 2.60 g sample of titanium metal chemically combines

san4es73 [151]

Answer:

For a: The empirical formula for the given compound is $TiCl_4$

For b: The percent by mass of titanium and chlorine in the sample is 25.55 % and 74.78 % respectively.

Explanation:

For a:

We are given:

Mass of Titanium = 2.60 g

Mass of sample = 10.31 g

Mass of Chlorine = 10.31 - 2.60 = 7.71 g

To formulate the empirical formula, we need to follow some steps:

Step 1: Converting the given masses into moles.

Moles of titanium = $\frac{\text{Given mass of Titanium}}{\text{Molar mass of Titanium}}=\frac{2.60g}{47.867g/mole}=0.054moles$

Moles of Chlorine = $\frac{\text{Given mass of Chlorine}}{\text{Molar mass of Chlorine}}=\frac{7.71g}{35.5g/mole}=0.217moles$

Step 2: Calculating the mole ratio of the given elements.

For the mole ratio, we divide each value of the moles by the smallest number of moles calculated which is 0.054 moles.

For Titanium = $\frac{0.054}{0.054}=1$

For Chlorine = $\frac{0.217}{0.054}=4.01\approx 4$

Step 3: Taking the mole ratio as their subscripts.

The ratio of Ti : Cl = 1 : 4

Hence, the empirical formula for the given compound is $TiCl_4$

For b:

To calculate the percentage by mass of substance in sample, we use the equation:

$\%\text{ composition of substance}=\frac{\text{Mass of substance}}{\text{Mass of sample}}\times 100$ .......(1)

For Titanium:

Mass of sample = 10.31 g

Mass of titanium = 2.60 g

Putting values in above equation, we get:

$\%\text{ composition of titanium}=\frac{2.60g}{10.31g}\times 100=25.22\%$

For Chlorine:

Mass of sample = 10.31 g

Mass of chlorine = 7.71 g

Putting values in above equation, we get:

$\%\text{ composition of chlorine}=\frac{7.71g}{10.31g}\times 100=74.78\%$

Hence, the percent by mass of titanium and chlorine in the sample is 25.55 % and 74.78 % respectively.

7 0

3 years ago

the water cycle is continuous process by which ______ moves from Earth's surface to the atmosphere and back again. This cycle is

LiRa [457]

Answer:

1-water 2-Sun 3-Gravity

8 0

2 years ago

Suppose a wave of visible light of wavelength equal to 555nm was traveling at a velocity of 55.5 cm/s past a point "A". How long

butalik [34]

Answer:

The answer is " $1 \times 10^{-6}\ s$ "

Explanation:

$v = velocity = 55.5 \ \frac{cm}{s} = 55.5 \times 10^{-2} \ \frac{m}{s}\\\\\lambda = wavelength = 555 \ nm = 555 \times 10^{-9}\ m\\\\\upsilon = frequency\\\\v = \lambda \upsilon \\\\\upsilon = \frac{v}{ \lambda}\\\\$